CHAPTER VIII.

THE EFFECTS OF VARIOUS OTHER SALTS AND ACIDS ON THE LEAVES.

Salts of sodium, potassium, and other alkaline, earthy, and metallic
salts—Summary on the action of these salts—Various acids—Summary on
their action.

Having found that the salts of ammonia were so powerful, I was led to
investigate the action of some other salts. It will be convenient,
first, to give a list of the substances tried (including forty-nine
salts and two metallic acids), divided into two columns, showing those
which cause inflection, and those which do not do so, or only
doubtfully. My experiments were made by placing half-minim drops on the
discs of leaves, or, more commonly, by immersing them in the solutions;
and sometimes by both methods. A summary of the results, with some
concluding remarks, will then be given. The action of various acids
will afterwards be described.

COLUMN 1 : SALTS CAUSING INFLECTION. COLUMN 2 : SALTS NOT CAUSING
INFLECTION.

(Arranged in Groups according to the Chemical Classification in Watts’
‘Dictionary of Chemistry.’)

Sodium carbonate, rapid inflection. : Potassium carbonate: slowly
poisonous. Sodium nitrate, rapid inflection. : Potassium nitrate:
somewhat poisonous. Sodium sulphate, moderately rapid inflection. :
Potassium sulphate. Sodium phosphate, very rapid inflection. :
Potassium phosphate. Sodium citrate, rapid inflection. : Potassium
citrate. Sodium oxalate; rapid inflection. Sodium chloride, moderately
rapid inflection. : Potassium chloride. [page 175]

COLUMN 1 : SALTS CAUSING INFLECTION. COLUMN 2 : SALTS NOT CAUSING
INFLECTION.

(Arranged in Groups according to the Chemical Classification in Watts’
‘Dictionary of Chemistry.’)

Sodium iodide, rather slow inflection. : Potassium iodide, a slight and
doubtful amount of inflection. Sodium bromide, moderately rapid
inflection. : Potassium bromide. Potassium oxalate, slow and doubtful
inflection. : Lithium nitrate, moderately rapid inflection. : Lithium
acetate. Caesium chloride, rather slow inflection. : Rubidium chloride.
Silver nitrate, rapid inflection: quick poison. : Cadmium chloride,
slow inflection. : Calcium acetate. Mercury perchloride, rapid
inflection: quick poison. : Calcium nitrate. : Magnesium acetate. :
Magnesium nitrate. : Magnesium chloride. : Magnesium sulphate. : Barium
acetate. : Barium nitrate. : Strontium acetate. : Strontium nitrate. :
Zinc chloride.

Aluminium chloride, slow and doubtful inflection. : Aluminium nitrate,
a trace of inflection. Gold chloride, rapid inflection: quick poison. :
Aluminium and potassium sulphate.

Tin chloride, slow inflection: poisonous. : Lead chloride.

Antimony tartrate, slow inflection: probably poisonous. Arsenious acid,
quick inflection: poisonous. Iron chloride, slow inflection: probably
poisonous. : Manganese chloride. Chromic acid, quick inflection: highly
poisonous. Copper chloride, rather slow in flection: poisonous. :
Cobalt chloride. Nickel chloride, rapid inflection: probably poisonous.
Platinum chloride, rapid inflection: poisonous. [page 176]

Sodium, Carbonate of (pure, given me by Prof. Hoffmann).—Half-minims
(.0296 ml.) of a solution of one part to 218 of water (2 grs. to 1 oz.)
were placed on the discs of twelve leaves. Seven of these became well
inflected; three had only two or three of their outer tentacles
inflected, and the remaining two were quite unaffected. But the dose,
though only the 1/480 of a grain (.135 mg.), was evidently too strong,
for three of the seven well-inflected leaves were killed. On the other
hand, one of the seven, which had only a few tentacles inflected,
re-expanded and seemed quite healthy after 48 hrs. By employing a
weaker solution (viz. one part to 437 of water, or 1 gr. to 1 oz.),
doses of 1/960 of a grain (.0675 mg.) were given to six leaves. Some of
these were affected in 37 m.; and in 8 hrs. the outer tentacles of all,
as well as the blades of two, were considerably inflected. After 23
hrs. 15 m. the tentacles had almost re-expanded, but the blades of the
two were still just perceptibly curved inwards. After 48 hrs. all six
leaves were fully re-expanded, and appeared perfectly healthy.

Three leaves were immersed, each in thirty minims of a solution of one
part to 875 of water (1 gr. to 2 oz.), so that each received 1/32 of a
grain (2.02 mg.); after 40 m. the three were much affected, and after 6
hrs. 45 m. the tentacles of all and the blade of one closely inflected.

Sodium, Nitrate of (pure).—Half-minims of a solution of one part to 437
of water, containing 1/960 of a grain (.0675 mg.), were placed on the
discs of five leaves. After 1 hr. 25 m. the tentacles of nearly all,
and the blade of one, were somewhat inflected. The inflection continued
to increase, and in 21 hrs. 15 m. the tentacles and the blades of four
of them were greatly affected, and the blade of the fifth to a slight
extent. After an additional 24 hrs. the four leaves still remained
closely inflected, whilst the fifth was beginning to expand. Four days
after the solution had been applied, two of the leaves had quite, and
one had partially, re-expanded; whilst the remaining two remained
closely inflected and appeared injured.

Three leaves were immersed, each in thirty minims of a solution of one
part to 875 of water; in 1 hr. there was great inflection, and after 8
hrs. 15 m. every tentacle and the blades of all three were most
strongly inflected.

Sodium, Sulphate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. After 5 hrs. 30 m. the
tentacles of three of them, (with the blade of one) were considerably;
and those of the other three slightly, inflected. After 21 hrs. the
inflection had a little decreased, [page 177] and in 45 hrs. the leaves
were fully expanded, appearing quite healthy.

Three leaves were immersed, each in thirty minims of a solution of one
part of the sulphate to 875 of water; after 1 hr. 30 m. there was some
inflection, which increased so much that in 8 hrs. 10 m. all the
tentacles and the blades of all three leaves were closely inflected.

Sodium, Phosphate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. The solution acted with
extraordinary rapidity, for in 8 m. the outer tentacles on several of
the leaves were much incurved. After 6 hrs. the tentacles of all six
leaves, and the blades of two, were closely inflected. This state of
things continued for 24 hrs., excepting that the blade of a third leaf
became incurved. After 48 hrs. all the leaves re-expanded. It is clear
that 1/960 of a grain of phosphate of soda has great power in causing
inflection.

Sodium, Citrate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves, but these were not
observed until 22 hrs. had elapsed. The sub-marginal tentacles of five
of them, and the blades of four, were then found inflected; but the
outer rows of tentacles were not affected. One leaf, which appeared
older than the others, was very little affected in any way. After 46
hrs. four of the leaves were almost re-expanded, including their
blades. Three leaves were also immersed, each in thirty minims of a
solution of one part of the citrate to 875 of water; they were much
acted on in 25 m.; and after 6 hrs. 35 m. almost all the tentacles,
including those of the outer rows, were inflected, but not the blades.

Sodium, Oxalate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of seven leaves; after 5 hrs. 30 m. the
tentacles of all, and the blades of most of them, were much affected.
In 22 hrs., besides the inflection of the tentacles, the blades of all
seven leaves were so much doubled over that their tips and bases almost
touched. On no other occasion have I seen the blades so strongly
affected. Three leaves were also immersed, each in thirty minims of a
solution of one part to 875 of water; after 30 m. there was much
inflection, and after 6 hrs. 35 m. the blades of two and the tentacles
of all were closely inflected.

Sodium, Chloride of (best culinary salt).—Half-minims of a solution of
one part to 218 of water were placed on the discs [page 178] of four
leaves. Two, apparently, were not at all affected in 48 hrs.; the third
had its tentacles slightly inflected; whilst the fourth had almost all
its tentacles inflected in 24 hrs., and these did not begin to
re-expand until the fourth day, and were not perfectly expanded on the
seventh day. I presume that this leaf was injured by the salt.
Half-minims of a weaker solution, of one part to 437 of water, were
then dropped on the discs of six leaves, so that each received 1/960 of
a grain. In 1 hr. 33 m. there was slight inflection; and after 5 hrs.
30 m. the tentacles of all six leaves were considerably, but not
closely, inflected. After 23 hrs. 15 m. all had completely re-expanded,
and did not appear in the least injured.

Three leaves were immersed, each in thirty minims of a solution of one
part to 875 of water, so that each received 1/32 of a grain, or 2.02
mg. After 1 hr. there was much inflection; after 8 hrs. 30 m. all the
tentacles and the blades of all three were closely inflected. Four
other leaves were also immersed in the solution, each receiving the
same amount of salt as before, viz. 1/32 of a grain. They all soon
became inflected; after 48 hrs. they began to re-expand, and appeared
quite uninjured, though the solution was sufficiently strong to taste
saline.

Sodium, Iodide of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. After 24 hrs. four of
them had their blades and many tentacles inflected. The other two had
only their submarginal tentacles inflected; the outer ones in most of
the leaves being but little affected. After 46 hrs. the leaves had
nearly re-expanded. Three leaves were also immersed, each in thirty
minims of a solution of one part to 875 of water. After 6 hrs. 30 m.
almost all the tentacles, and the blade of one leaf, were closely
inflected.

Sodium, Bromide of.—Half-minims of a solution of one part to 437 of
water were placed on six leaves. After 7 hrs. there was some
inflection; after 22 hrs. three of the leaves had their blades and most
of their tentacles inflected; the fourth leaf was very slightly, and
the fifth and sixth hardly at all, affected. Three leaves were also
immersed, each in thirty minims of a solution of one part to 875 of
water; after 40 m. there was some inflection; after 4 hrs. the
tentacles of all three leaves and the blades of two were inflected.
These leaves were then placed in water, and after 17 hrs. 30 m. two of
them were almost completely, and the third partially, re-expanded; so
that apparently they were not injured. [page 179]

Potassium, Carbonate of (pure).—Half-minims of a solution of one part
to 437 of water were placed on six leaves. No effect was produced in 24
hrs.; but after 48 hrs. some of the leaves had their tentacles, and one
the blade, considerably inflected. This, however, seemed the result of
their being injured; for on the third day after the solution was given,
three of the leaves were dead, and one was very unhealthy; the other
two were recovering, but with several of their tentacles apparently
injured, and these remained permanently inflected. It is evident that
the 1/960 of a grain of this salt acts as a poison. Three leaves were
also immersed, each in thirty minims of a solution of one part to 875
of water, though only for 9 hrs.; and, very differently from what
occurs with the salts of soda, no inflection ensued.

Potassium, Nitrate of.—Half-minims of a strong solution, of one part to
109 of water (4 grs. to 1 oz.), were placed on the discs of four
leaves; two were much injured, but no inflection ensued. Eight leaves
were treated in the same manner, with drops of a weaker solution, of
one part to 218 of water. After 50 hrs. there was no inflection, but
two of the leaves seemed injured. Five of these leaves were
subsequently tested with drops of milk and a solution of gelatine on
their discs, and only one became inflected; so that the solution of the
nitrate of the above strength, acting for 50 hrs., apparently had
injured or paralysed the leaves. Six leaves were then treated in the
same manner with a still weaker solution, of one part to 437 of water,
and these, after 48 hrs., were in no way affected, with the exception
of perhaps a single leaf. Three leaves were next immersed for 25 hrs.,
each in thirty minims of a solution of one part to 875 of water, and
this produced no apparent effect. They were then put into a solution of
one part of carbonate of ammonia to 218 of water; the glands were
immediately blackened, and after 1 hr. there was some inflection, and
the protoplasmic contents of the cells became plainly aggregated. This
shows that the leaves had not been much injured by their immersion for
25 hrs. in the nitrate.

Potassium, Sulphate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. After 20 hrs. 30 m. no
effect was produced; after an additional 24 hrs. three remained quite
unaffected; two seemed injured, and the sixth seemed almost dead with
its tentacles inflected. Nevertheless, after two additional days, all
six leaves recovered. The immersion of three leaves for 24 hrs., each
in thirty minims of [page 180] a solution of one part to 875 of water,
produced no apparent effect. They were then treated with the same
solution of carbonate of ammonia, with the same result as in the case
of the nitrate of potash.

Potassium, Phosphate of.—Half-minims of a solution of one part to 437
of water were placed on the discs of six leaves, which were observed
during three days; but no effect was produced. The partial drying up of
the fluid on the disc slightly drew together the tentacles on it, as
often occurs in experiments of this kind. The leaves on the third day
appeared quite healthy.

Potassium, Citrate of.—Half-minims of a solution of one part to 437 of
water, left on the discs of six leaves for three days, and the
immersion of three leaves for 9 hrs., each in 30 minims of a solution
of one part to 875 of water, did not produce the least effect.

Potassium, Oxalate of.—Half-minims were placed on different occasions
on the discs of seventeen leaves; and the results perplexed me much, as
they still do. Inflection supervened very slowly. After 24 hrs. four
leaves out of the seventeen were well inflected, together with the
blades of two; six were slightly affected, and seven not at all. Three
leaves of one lot were observed for five days, and all died; but in
another lot of six, all excepting one looked healthy after four days.
Three leaves were immersed during 9 hrs., each in 30 minims of a
solution of one part to 875 of water, and were not in the least
affected; but they ought to have been observed for a longer time.

Potassium, Chloride of. Neither half-minims of a solution of one part
to 437 of water; left on the discs of six leaves for three days, nor
the immersion of three leaves during 25 hrs., in 30 minims of a
solution of one part to 875 of water, produced the least effect. The
immersed leaves were then treated with carbonate of ammonia, as
described under nitrate of potash, and with the same result.

Potassium, Iodide of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of seven leaves. In 30 m. one leaf had
the blade inflected; after some hours three leaves had most of their
submarginal tentacles moderately inflected; the remaining three being
very slightly affected. Hardly any of these leaves had their outer
tentacles inflected. After 21 hrs. all re-expanded, excepting two which
still had a few submarginal tentacles inflected. Three leaves were next
[page 181] immersed for 8 hrs. 40 m., each in 30 minims of a solution
of one part to 875 of water, and were not in the least affected. I do
not know what to conclude from this conflicting evidence; but it is
clear that the iodide of potassium does not generally produce any
marked effect.

Potassium, Bromide of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves; after 22 hrs. one had its
blade and many tentacles inflected, but I suspect that an insect might
have alighted on it and then escaped; the five other leaves were in no
way affected. I tested three of these leaves with bits of meat, and
after 24 hrs. they became splendidly inflected. Three leaves were also
immersed for 21 hrs. in 30 minims of a solution of one part to 875 of
water; but they were not at all affected, excepting that the glands
looked rather pale.

Lithium, Acetate of.—Four leaves were immersed together in a vessel
containing 120 minims of a solution of one part to 437 of water; so
that each received, if the leaves absorbed equally, 1/16 of a grain.
After 24 hrs. there was no inflection. I then added, for the sake of
testing the leaves, some strong solution (viz. 1 gr. to 20 oz., or one
part to 8750 of water) of phosphate of ammonia, and all four became in
30 m. closely inflected.

Lithium, Nitrate of.—Four leaves were immersed, as in the last case, in
120 minims of a solution of one part to 437 of water; after 1 h. 30 m.
all four were a little, and after 24 hrs. greatly, inflected. I then
diluted the solution with some water, but they still remained somewhat
inflected on the third day.

Caesium, Chloride of.—Four leaves were immersed, as above, in 120
minims of a solution of one part to 437 of water. After 1 hr. 5 m. the
glands were darkened; after 4 hrs. 20 m. there was a trace of
inflection; after 6 hrs. 40 m. two leaves were greatly, but not
closely, and the other two considerably inflected. After 22 hrs. the
inflection was extremely great, and two had their blades inflected. I
then transferred the leaves into water, and in 46 hrs. from their first
immersion they were almost re-expanded.

Rubidium, Chloride of.—Four leaves which were immersed, as above, in
120 minims of a solution of one part to 437 of water, were not acted on
in 22 hrs. I then added some of the strong solution (1 gr. to 20 oz.)
of phosphate of ammonia, and in 30 m. all were immensely inflected.

Silver, Nitrate of.—Three leaves were immersed in ninety [page 182]
minims of a solution of one part to 437 of water; so that each
received, as before, 1/16 of a grain. After 5 m. slight inflection, and
after 11 m. very strong inflection, the glands becoming excessively
black; after 40 m. all the tentacles were closely inflected. After 6
hrs. the leaves were taken out of the solution, washed, and placed in
water; but next morning they were evidently dead.

Calcium, Acetate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 24 hrs. none of the
tentacles were inflected, excepting a few where the blade joined the
petiole; and this may have been caused by the absorption of the salt by
the cut-off end of the petiole. I then added some of the solution (1
gr. to 20 oz.) of phosphate of ammonia, but this to my surprise excited
only slight inflection, even after 24 hrs. Hence it would appear that
the acetate had rendered the leaves torpid.

Calcium, Nitrate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water, but were not affected in 24 hrs.
I then added some of the solution of phosphate of ammonia (1 gr. to 20
oz.), but this caused only very slight inflection after 24 hrs. A fresh
leaf was next put into a mixed solution of the above strengths of the
nitrate of calcium and phosphate of ammonia, and it became closely
inflected in between 5 m. and 10 m. Half-minims of a solution of one
part of the nitrate of calcium to 218 of water were dropped on the
discs of three leaves, but produced no effect.

Magnesium, Acetate, Nitrate, and Chloride of.—Four leaves were immersed
in 120 minims of solutions, of one part to 437 of water, of each of
these three salts; after 6 hrs. there was no inflection; but after 22
hrs. one of the leaves in the acetate was rather more inflected than
generally occurs from an immersion for this length of time in water.
Some of the solution (1 gr. to 20 oz.) of phosphate of ammonia was then
added to the three solutions. The leaves in the acetate mixed with the
phosphate underwent some inflection; and this was well pronounced after
24 hrs. Those in the mixed nitrate were decidedly inflected in 4 hrs.
30 m., but the degree of inflection did not afterwards much increase;
whereas the four leaves in the mixed chloride were greatly inflected in
a few minutes, and after 4 hrs. had almost every tentacle closely
inflected. We thus see that the acetate and nitrate of magnesium injure
the leaves, or at least prevent the subsequent action of phosphate of
ammonia; whereas the chloride has no such tendency. [page 183]

Magnesium, Sulphate of.—Half-minims of a solution of one part to 218 of
water were placed on the discs of ten leaves, and produced no effect.

Barium, Acetate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water, and after 22 hrs. there was no
inflection, but the glands were blackened. The leaves were then placed
in a solution (1 gr. to 20 oz.) of phosphate of ammonia, which caused
after 26 hrs. only a little inflection in two of the leaves.

Barium, Nitrate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; and after 22 hrs. there was no
more than that slight degree of inflection, which often follows from an
immersion of this length in pure water. I then added some of the same
solution of phosphate of ammonia, and after 30 m. one leaf was greatly
inflected, two others moderately, and the fourth not at all. The leaves
remained in this state for 24 hrs.

Strontium, Acetate of.—Four leaves, immersed in 120 minims of a
solution of one part to 437 of water, were not affected in 22 hrs. They
were then placed in some of the same solution of phosphate of ammonia,
and in 25 m. two of them were greatly inflected; after 8 hrs. the third
leaf was considerably inflected, and the fourth exhibited a trace of
inflection. They were in the same state next morning.

Strontium, Nitrate of.—Five leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 22 hrs. there was some
slight inflection, but not more than sometimes occurs with leaves in
water. They were then placed in the same solution of phosphate of
ammonia; after 8 hrs. three of them were moderately inflected, as were
all five after 24 hrs.; but not one was closely inflected. It appears
that the nitrate of strontium renders the leaves half torpid.

Cadmium, Chloride of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water; after 5 hrs. 20 m. slight
inflection occurred, which increased during the next three hours. After
24 hrs. all three leaves had their tentacles well inflected, and
remained so for an additional 24 hrs.; glands not discoloured.

Mercury, Perchloride of.—Three leaves were immersed in ninety minims of
a solution of one part to 437 of water; after 22 m. there was some
slight inflection, which in 48 m. became well pronounced; the glands
were now blackened. After 5 hrs. 35 m. all the tentacles closely
inflected; after 24 hrs. still [page 184] inflected and discoloured.
The leaves were then removed and left for two days in water; but they
never re-expanded, being evidently dead.

Zinc, Chloride of.—Three leaves immersed in ninety minims of a solution
of one part to 437 of water were not affected in 25 hrs. 30 m.

Aluminium, Chloride of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 7 hrs. 45 m. no inflection;
after 24 hrs. one leaf rather closely, the second moderately, the third
and fourth hardly at all, inflected. The evidence is doubtful, but I
think some power in slowly causing inflection must be attributed to
this salt. These leaves were then placed in the solution (1 gr. to 20
oz.) of phosphate of ammonia, and after 7 hrs. 30 m. the three, which
had been but little affected by the chloride, became rather closely
inflected.

Aluminium, Nitrate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 7 hrs. 45 m. there was only
a trace of inflection; after 24 hrs. one leaf was moderately inflected.
The evidence is here again doubtful, as in the case of the chloride of
aluminium. The leaves were then transferred to the same solution, as
before, of phosphate of ammonia; this produced hardly any effect in 7
hrs. 30 m.; but after 25 hrs. one leaf was pretty closely inflected,
the three others very slightly, perhaps not more so than from water.

Aluminium and Potassium, Sulphate of (common alum).—Half-minims of a
solution of the usual strength were placed on the discs of nine leaves,
but produced no effect.

Gold, Chloride of.—Seven leaves were immersed in so much of a solution
of one part to 437 of water that each received 30 minims, containing
1/16 of a grain, or 4.048 mg., of the chloride. There was some
inflection in 8 m., which became extreme in 45 m. In 3 hrs. the
surrounding fluid was coloured purple, and the glands were blackened.
After 6 hrs. the leaves were transferred to water; next morning they
were found discoloured and evidently killed. The secretion decomposes
the chloride very readily; the glands themselves becoming coated with
the thinnest layer of metallic gold, and particles float about on the
surface of the surrounding fluid.

Lead, Chloride of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water. After 23 hrs. there was not a
trace of inflection; the glands were not blackened, and the leaves did
not appear injured. They were then trans- [page 185] ferred to the
solution (1 gr. to 20 oz.) of phosphate of ammonia, and after 24 hrs.
two of them were somewhat, the third very little, inflected; and they
thus remained for another 24 hrs.

Tin, Chloride of.—Four leaves were immersed in 120 minims of a solution
of about one part (all not being dissolved) to 437 of water. After 4
hrs. no effect; after 6 hrs. 30 m. all four leaves had their
submarginal tentacles inflected; after 22 hrs. every single tentacle
and the blades were closely inflected. The surrounding fluid was now
coloured pink. The leaves were washed and transferred to water, but
next morning were evidently dead. This chloride is a deadly poison, but
acts slowly.

Antimony, Tartrate of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water. After 8 hrs. 30 m. there was
slight inflection; after 24 hrs. two of the leaves were closely, and
the third moderately, inflected; glands not much darkened. The leaves
were washed and placed in water, but they remained in the same state
for 48 additional hours. This salt is probably poisonous, but acts
slowly.

Arsenious Acid.—A solution of one part to 437 of water; three leaves
were immersed in ninety minims; in 25 m. considerable inflection; in 1
h. great inflection; glands not discoloured. After 6 hrs. the leaves
were transferred to water; next morning they looked fresh, but after
four days were pale-coloured, had not re-expanded, and were evidently
dead.

Iron, Chloride of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water; in 8 hrs. no inflection; but
after 24 hrs. considerable inflection; glands blackened; fluid coloured
yellow, with floating flocculent particles of oxide of iron. The leaves
were then placed in water; after 48 hrs. they had re-expanded a very
little, but I think were killed; glands excessively black.

Chromic Acid.—One part to 437 of water; three leaves were immersed in
ninety minims; in 30 m. some, and in 1 hr. considerable, inflection;
after 2 hrs. all the tentacles closely inflected, with the glands
discoloured. Placed in water, next day leaves quite discoloured and
evidently killed.

Manganese, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; after 22 hrs. no more inflection
than often occurs in water; glands not blackened. The leaves were then
placed in the usual solution of phosphate of ammonia, but no inflection
was caused even after 48 hrs.

Copper, Chloride of.—Three leaves immersed in ninety minims [page 186]
of a solution of one part to 437 of water; after 2 hrs. some
inflection; after 3 hrs. 45 m. tentacles closely inflected, with the
glands blackened. After 22 hrs. still closely inflected, and the leaves
flaccid. Placed in pure water, next day evidently dead. A rapid poison.

Nickel, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; in 25 m. considerable inflection,
and in 3 hrs. all the tentacles closely inflected. After 22 hrs. still
closely inflected; most of the glands, but not all, blackened. The
leaves were then placed in water; after 24 hrs. remained inflected;
were somewhat discoloured, with the glands and tentacles dingy red.
Probably killed.

Cobalt, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; after 23 hrs. there was not a
trace of inflection, and the glands were not more blackened than often
occurs after an equally long immersion in water.

Platinum, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; in 6 m. some inflection, which
became immense after 48 m. After 3 hrs. the glands were rather pale.
After 24 hrs. all the tentacles still closely inflected; glands
colourless; remained in same state for four days; leaves evidently
killed.]

Concluding Remarks on the Action of the foregoing Salts.—Of the
fifty-one salts and metallic acids which were tried, twenty-five caused
the tentacles to be inflected, and twenty-six had no such effect, two
rather doubtful cases occurring in each series. In the table at the
head of this discussion, the salts are arranged according to their
chemical affinities; but their action on Drosera does not seem to be
thus governed. The nature of the base is far more important, as far as
can be judged from the few experiments here given, than that of the
acid; and this is the conclusion at which physiologists have arrived
with respect to animals. We see this fact illustrated in all the nine
salts of soda causing inflection, and in not being poisonous except
when given in large doses; whereas seven of [page 187] the
corresponding salts of potash do not cause inflection, and some of them
are poisonous. Two of them, however, viz. the oxalate and iodide of
potash, slowly induced a slight and rather doubtful amount of
inflection. This difference between the two series is interesting, as
Dr. Burdon Sanderson informs me that sodium salts may be introduced in
large doses into the circulation of mammals without any injurious
effects; whilst small doses of potassium salts cause death by suddenly
arresting the movements of the heart. An excellent instance of the
different action of the two series is presented by the phosphate of
soda quickly causing vigorous inflection, whilst phosphate of potash is
quite inefficient. The great power of the former is probably due to the
presence of phosphorus, as in the cases of phosphate of lime and of
ammonia. Hence we may infer that Drosera cannot obtain phosphorus from
the phosphate of potash. This is remarkable, as I hear from Dr. Burdon
Sanderson that phosphate of potash is certainly decomposed within the
bodies of animals. Most of the salts of soda act very rapidly; the
iodide acting slowest. The oxalate, nitrate, and citrate seem to have a
special tendency to cause the blade of the leaf to be inflected. The
glands of the disc, after absorbing the citrate, transmit hardly any
motor impulse to the outer tentacles; and in this character the citrate
of soda resembles the citrate of ammonia, or a decoction of
grass-leaves; these three fluids all acting chiefly on the blade.

It seems opposed to the rule of the preponderant influence of the base
that the nitrate of lithium causes moderately rapid inflection, whereas
the acetate causes none; but this metal is closely allied to sodium
[page 188] and potassium,* which act so differently; therefore we might
expect that its action would be intermediate. We see, also, that
caesium causes inflection, and rubidium does not; and these two metals
are allied to sodium and potassium. Most of the earthy salts are
inoperative. Two salts of calcium, four of magnesium, two of barium,
and two of strontium, did not cause any inflection, and thus follow the
rule of the preponderant power of the base. Of three salts of
aluminium, one did not act, a second showed a trace of action, and the
third acted slowly and doubtfully, so that their effects are nearly
alike.

Of the salts and acids of ordinary metals, seventeen were tried, and
only four, namely those of zinc, lead, manganese, and cobalt, failed to
cause inflection. The salts of cadmium, tin, antimony, and iron, act
slowly; and the three latter seem more or less poisonous. The salts of
silver, mercury, gold, copper, nickel, and platinum, chromic and
arsenious acids, cause great inflection with extreme quickness, and are
deadly poisons. It is surprising, judging from animals, that lead and
barium should not be poisonous. Most of the poisonous salts make the
glands black, but chloride of platinum made them very pale. I shall
have occasion, in the next chapter, to add a few remarks on the
different effects of phosphate of ammonia on leaves previously immersed
in various solutions.

I will first give, as in the case of the salts, a list of the
twenty-four acids which were tried, divided into two series, according
as they cause or do not cause

* Miller’s ‘Elements of Chemistry,’ 3rd edit. pp. 337, 448. [page 189]

inflection. After describing the experiments, a few concluding remarks
will be added.

ACIDS, MUCH DILUTED, WHICH CAUSE INFLECTION.

1. Nitric, strong inflection; poisonous. 2. Hydrochloric, moderate and
slow inflection; not poisonous. 3. Hydriodic, strong inflection;
poisonous. 4. Iodic, strong inflection; poisonous. 5. Sulphuric, strong
inflection; somewhat poisonous. 6. Phosphoric, strong inflection;
poisonous. 7. Boracic; moderate and rather slow inflection; not
poisonous. 8. Formic, very slight inflection; not poisonous. 9. Acetic,
strong and rapid inflection; poisonous. 10. Propionic, strong but not
very rapid inflection; poisonous. 11. Oleic, quick inflection; very
poisonous. 12. Carbolic, very slow inflection; poisonous. 13. Lactic,
slow and moderate inflection; poisonous. 14. Oxalic, moderately quick
inflection; very poisonous. 15. Malic, very slow but considerable
inflection; not poisonous. 16. Benzoic, rapid inflection; very
poisonous. 17. Succinic, moderately quick inflection: moderately
poisonous. 18. Hippuric, rather slow inflection; poisonous. 19.
Hydrocyanic, rather rapid inflection; very poisonous.

ACIDS, DILUTED TO THE SAME DEGREE, WHICH DO NOT CAUSE INFLECTION.

1. Gallic; not poisonous. 2. Tannic; not poisonous. 3. Tartaric; not
poisonous. 4. Citric; not poisonous. 5. Uric; (?) not poisonous.

Nitric Acid.—Four leaves were placed, each in thirty minims of one part
by weight of the acid to 437 of water, so that each received 1/16 of a
grain, or 4.048 mg. This strength was chosen for this and most of the
following experiments, as it is the same [page 190] as that of most of
the foregoing saline solutions. In 2 hrs. 30 m. some of the leaves were
considerably, and in 6 hrs. 30 m. all were immensely, inflected, as
were their blades. The surrounding fluid was slightly coloured pink,
which always shows that the leaves have been injured. They were then
left in water for three days; but they remained inflected and were
evidently killed. Most of the glands had become colourless. Two leaves
were then immersed, each in thirty minims of one part to 1000 of water;
in a few hours there was some inflection; and after 24 hrs. both leaves
had almost all their tentacles and blades inflected; they were left in
water for three days, and one partially re-expanded and recovered. Two
leaves were next immersed, each in thirty minims of one part to 2000 of
water; this produced very little effect, except that most of the
tentacles close to the summit of the petiole were inflected, as if the
acid had been absorbed by the cut-off end.

Hydrochloric Acid.—One part to 437 of water; four leaves were immersed
as before, each in thirty minims. After 6 hrs. only one leaf was
considerably inflected. After 8 hrs. 15 m. one had its tentacles and
blade well inflected; the other three were moderately inflected, and
the blade of one slightly. The surrounding fluid was not coloured at
all pink. After 25 hrs. three of these four leaves began to re-expand,
but their glands were of a pink instead of a red colour; after two more
days they fully re-expanded; but the fourth leaf remained inflected,
and seemed much injured or killed, with its glands white. Four leaves
were then treated, each with thirty minims of one part to 875 of water;
after 21 hrs. they were moderately inflected; and on being transferred
to water, fully re-expanded in two days, and seemed quite healthy.

Hydriodic Acid.—One to 437 of water; three leaves were immersed as
before, each in thirty minims. After 45 m. the glands were discoloured,
and the surrounding fluid became pinkish, but there was no inflection.
After 5 hrs. all the tentacles were closely inflected; and an immense
amount of mucus was secreted, so that the fluid could be drawn out into
long ropes. The leaves were then placed in water, but never
re-expanded, and were evidently killed. Four leaves were next immersed
in one part to 875 of water; the action was now slower, but after 22
hrs. all four leaves were closely inflected, and were affected in other
respects as above described. These leaves did not re-expand, though
left for four days in water. This acid acts far more powerfully than
hydrochloric, and is poisonous.

Iodic Acid.—One to 437 of water; three leaves were immersed, [page 191]
each in thirty minims; after 3 hrs. strong inflection; after 4 hrs.
glands dark brown; after 8 hrs. 30 m. close inflection, and the leaves
had become flaccid; surrounding fluid not coloured pink. These leaves
were then placed in water, and next day were evidently dead.

Sulphuric Acid.—One to 437 of water; four leaves were immersed, each in
thirty minims; after 4 hrs. great inflection; after 6 hrs. surrounding
fluid just tinged pink; they were then placed in water, and after 46
hrs. two of them were still closely inflected, two beginning to
re-expand; many of the glands colourless. This acid is not so poisonous
as hydriodic or iodic acids.

Phosphoric Acid.—One to 437 of water; three leaves were immersed
together in ninety minims; after 5 hrs. 30 m. some inflection, and some
glands colourless; after 8 hrs. all the tentacles closely inflected,
and many glands colourless; surrounding fluid pink. Left in water for
two days and a half, remained in the same state and appeared dead.

Boracic Acid.—One to 437 of water; four leaves were immersed together
in 120 minims; after 6 hrs. very slight inflection; after 8 hrs. 15 m.
two were considerably inflected, the other two slightly. After 24 hrs.
one leaf was rather closely inflected, the second less closely, the
third and fourth moderately. The leaves were washed and put into water;
after 24 hrs. they were almost fully re-expanded and looked healthy.
This acid agrees closely with hydrochloric acid of the same strength in
its power of causing inflection, and in not being poisonous.

Formic Acid.—Four leaves were immersed together in 120 minims of one
part to 437 of water; after 40 m. slight, and after 6 hrs. 30 m. very
moderate inflection; after 22 hrs. only a little more inflection than
often occurs in water. Two of the leaves were then washed and placed in
a solution (1 gr. to 20 oz.) of phosphate of ammonia; after 24 hrs.
they were considerably inflected, with the contents of their cells
aggregated, showing that the phosphate had acted, though not to the
full and ordinary degree.

Acetic Acid.—Four leaves were immersed together in 120 minims of one
part to 437 of water. In 1 hr. 20 m. the tentacles of all four and the
blades of two were greatly inflected. After 8 hrs. the leaves had
become flaccid, but still remained closely inflected, the surrounding
fluid being coloured pink. They were then washed and placed in water;
next morning they were still inflected and of a very dark red colour,
but with their glands colourless. After another day they were
dingy-coloured, and [page 192] evidently dead. This acid is far more
powerful than formic, and is highly poisonous. Half-minim drops of a
stronger mixture (viz. one part by measure to 320 of water) were placed
on the discs of five leaves; none of the exterior tentacles, only those
on the borders of the disc which actually absorbed the acid, became
inflected. Probably the dose was too strong and paralysed the leaves,
for drops of a weaker mixture caused much inflection; nevertheless the
leaves all died after two days.

Propionic Acid.—Three leaves were immersed in ninety minims of a
mixture of one part to 437 of water; in 1 hr. 50 m. there was no
inflection; but after 3 hrs. 40 m. one leaf was greatly inflected, and
the other two slightly. The inflection continued to increase, so that
in 8 hrs. all three leaves were closely inflected. Next morning, after
20 hrs., most of the glands were very pale, but some few were almost
black. No mucus had been secreted, and the surrounding fluid was only
just perceptibly tinted of a pale pink. After 46 hrs. the leaves became
slightly flaccid and were evidently killed, as was afterwards proved to
be the case by keeping them in water. The protoplasm in the closely
inflected tentacles was not in the least aggregated, but towards their
bases it was collected in little brownish masses at the bottoms of the
cells. This protoplasm was dead, for on leaving the leaf in a solution
of carbonate of ammonia, no aggregation ensued. Propionic acid is
highly poisonous to Drosera, like its ally acetic acid, but induces
inflection at a much slower rate.

Oleic Acid (given me by Prof. Frankland).—Three leaves were immersed in
this acid; some inflection was almost immediately caused, which
increased slightly, but then ceased, and the leaves seemed killed. Next
morning they were rather shrivelled, and many of the glands had fallen
off the tentacles. Drops of this acid were placed on the discs of four
leaves; in 40 m. all the tentacles were greatly inflected, excepting
the extreme marginal ones; and many of these after 3 hrs. became
inflected. I was led to try this acid from supposing that it was
present (which does not seem to be the case)* in olive oil, the action
of which is anomalous. Thus drops of this oil placed on the disc do not
cause the outer tentacles to be inflected; yet when minute drops were
added to the secretion surrounding the glands of the outer tentacles,
these were occasionally, but by no means always, inflected. Two leaves
were also immersed in this oil, and there

* See articles on Glycerine and Oleic Acid in Watts’ ‘Dict. of
Chemistry.’ [page 193]

was no inflection for about 12 hrs.; but after 23 hrs. almost all the
tentacles were inflected. Three leaves were likewise immersed in
unboiled linseed oil, and soon became somewhat, and in 3 hrs. greatly,
inflected. After 1 hr. the secretion round the glands was coloured
pink. I infer from this latter fact that the power of linseed oil to
cause inflection cannot be attributed to the albumin which it is said
to contain.

Carbolic Acid.—Two leaves were immersed in sixty minims of a solution
of 1 gr. to 437 of water; in 7 hrs. one was slightly, and in 24 hrs.
both were closely, inflected, with a surprising amount of mucus
secreted. These leaves were washed and left for two days in water; they
remained inflected; most of their glands became pale, and they seemed
dead. This acid is poisonous, but does not act nearly so rapidly or
powerfully as might have been expected from its known destructive power
on the lowest organisms. Half-minims of the same solution were placed
on the discs of three leaves; after 24 hrs. no inflection of the outer
tentacles ensued, and when bits of meat were given them, they became
fairly well inflected. Again half-minims of a stronger solution, of one
part to 218 of water, were placed on the discs of three leaves; no
inflection of the outer tentacles ensued; bits of meat were then given
as before; one leaf alone became well inflected, the discal glands of
the other two appearing much injured and dry. We thus see that the
glands of the discs, after absorbing this acid, rarely transmit any
motor impulse to the outer tentacles; though these, when their own
glands absorb the acid, are strongly acted on.

Lactic Acid.—Three leaves were immersed in ninety minims of one part to
437 of water. After 48 m. there was no inflection, but the surrounding
fluid was coloured pink; after 8 hrs. 30 m. one leaf alone was a little
inflected, and almost all the glands on all three leaves were of a very
pale colour. The leaves were then washed and placed in a solution (1
gr. to 20 oz.) of phosphate of ammonia; after about 16 hrs. there was
only a trace of inflection. They were left in the phosphate for 48
hrs., and remained in the same state, with almost all their glands
discoloured. The protoplasm within the cells was not aggregated, except
in a very few tentacles, the glands of which were not much discoloured.
I believe, therefore, that almost all the glands and tentacles had been
killed by the acid so suddenly that hardly any inflection was caused.
Four leaves were next immersed in 120 minims of a weaker solution, of
one part to 875 of water; after 2 hrs. 30 m. the surrounding fluid was
quite pink; the glands were pale, but [page 194] there was no
inflection; after 7 hrs. 30 m. two of the leaves showed some
inflection, and the glands were almost white; after 21 hrs. two of the
leaves were considerably inflected, and a third slightly; most of the
glands were white, the others dark red. After 45 hrs. one leaf had
almost every tentacle inflected; a second a large number; the third and
fourth very few; almost all the glands were white, excepting those on
the discs of two of the leaves, and many of these were very dark red.
The leaves appeared dead. Hence lactic acid acts in a very peculiar
manner, causing inflection at an extraordinarily slow rate, and being
highly poisonous. Immersion in even weaker solutions, viz. of one part
to 1312 and 1750 of water, apparently killed the leaves (the tentacles
after a time being bowed backwards), and rendered the glands white, but
caused no inflection.

Gallic, Tannic, Tartaric, and Citric Acids.—One part to 437 of water.
Three or four leaves were immersed, each in thirty minims of these four
solutions, so that each leaf received 1/16 of a grain, or 4.048 mg. No
inflection was caused in 24 hrs., and the leaves did not appear at all
injured. Those which had been in the tannic and tartaric acids were
placed in a solution (1 gr. to 20 oz.) of phosphate of ammonia, but no
inflection ensued in 24 hrs. On the other hand, the four leaves which
had been in the citric acid, when treated with the phosphate, became
decidedly inflected in 50 m. and strongly inflected after 5 hrs., and
so remained for the next 24 hrs.

Malic Acid.—Three leaves were immersed in ninety minims of a solution
of one part to 437 of water; no inflection was caused in 8 hrs. 20 m.,
but after 24 hrs. two of them were considerably, and the third
slightly, inflected—more so than could be accounted for by the action
of water. No great amount of mucus was secreted. They were then placed
in water, and after two days partially re-expanded. Hence this acid is
not poisonous.

Oxalic Acid.—Three leaves were immersed in ninety minims of a solution
of 1 gr. to 437 of water; after 2 hrs. 10 m. there was much inflection;
glands pale; the surrounding fluid of a dark pink colour; after 8 hrs.
excessive inflection. The leaves were then placed in water; after about
16 hrs. the tentacles were of a very dark red colour, like those of the
leaves in acetic acid. After 24 additional hours, the three leaves were
dead and their glands colourless.

Benzoic Acid.—Five leaves were immersed, each in thirty minims of a
solution of 1 gr. to 437 of water. This solution was so weak that it
only just tasted acid, yet, as we shall see, was highly poisonous to
Drosera. After 52 m. the submarginal [page 195] tentacles were somewhat
inflected, and all the glands very pale-coloured; the surrounding fluid
was coloured pink. On one occasion the fluid became pink in the course
of only 12 m., and the glands as white as if the leaf had been dipped
in boiling water. After 4 hrs. much inflection; but none of the
tentacles were closely inflected, owing, as I believe, to their having
been paralysed before they had time to complete their movement. An
extraordinary quantity of mucus was secreted. Some of the leaves were
left in the solution; others, after an immersion of 6 hrs. 30 m., were
placed in water. Next morning both lots were quite dead; the leaves in
the solution being flaccid, those in the water (now coloured yellow) of
a pale brown tint, and their glands white.

Succinic Acid.—Three leaves were immersed in ninety minims of a
solution of 1 gr. to 437 of water; after 4 hrs. 15 m. considerable and
after 23 hrs. great inflection; many of the glands pale; fluid coloured
pink. The leaves were then washed and placed in water; after two days
there was some re-expansion, but many of the glands were still white.
This acid is not nearly so poisonous as oxalic or benzoic.

Uric Acid.—Three leaves were immersed in 180 minims of a solution of 1
gr. to 875 of warm water, but all the acid was not dissolved; so that
each received nearly 1/16 of a grain. After 25 m. there was some slight
inflection, but this never increased; after 9 hrs. the glands were not
discoloured, nor was the solution coloured pink; nevertheless much
mucus was secreted. The leaves were then placed in water, and by next
morning fully re-expanded. I doubt whether this acid really causes
inflection, for the slight movement which at first occurred may have
been due to the presence of a trace of albuminous matter. But it
produces some effect, as shown by the secretion of so much mucus.

Hippuric Acid.—Four leaves were immersed in 120 minims of a solution of
1 gr. to 437 of water. After 2 hrs. the fluid was coloured pink; glands
pale, but no inflection. After 6 hrs. some inflection; after 9 hrs. all
four leaves greatly inflected; much mucus secreted; all the glands very
pale. The leaves were then left in water for two days; they remained
closely inflected, with their glands colourless, and I do not doubt
were killed.

Hydrocyanic Acid.—Four leaves were immersed, each in thirty minims of
one part to 437 of water; in 2 hrs. 45 m. all the tentacles were
considerably inflected, with many of the glands pale; after 3 hrs. 45
m. all strongly inflected, and the surrounding fluid coloured pink;
after 6 hrs. all closely inflected. After [page 196] an immersion of 8
hrs. 20 m. the leaves were washed and placed in water; next morning,
after about 16 hrs., they were still inflected and discoloured; on the
succeeding day they were evidently dead. Two leaves were immersed in a
stronger mixture, of one part to fifty of water; in 1 hr. 15 m. the
glands became as white as porcelain, as if they had been dipped in
boiling water; very few of the tentacles were inflected; but after 4
hrs. almost all were inflected. These leaves were then placed in water,
and next morning were evidently dead. Half-minim drops of the same
strength (viz. one part to fifty of water) were next placed on the
discs of five leaves; after 21 hrs. all the outer tentacles were
inflected, and the leaves appeared much injured. I likewise touched the
secretion round a large number of glands with minute drops (about 1/20
of a minim, or .00296 ml.) of Scheele’s mixture (6 per cent.); the
glands first became bright red, and after 3 hrs. 15 m. about two-thirds
of the tentacles bearing these glands were inflected, and remained so
for the two succeeding days, when they appeared dead.]

Concluding Remarks on the Action of Acids.—It is evident that acids
have a strong tendency to cause the inflection of the tentacles;* for
out of the twenty-four acids tried, nineteen thus acted, either rapidly
and energetically, or slowly and slightly. This fact is remarkable, as
the juices of many plants contain more acid, judging by the taste, than
the solutions employed in my experiments. From the powerful effects of
so many acids on Drosera, we are led to infer that those naturally
contained in the tissues of this plant, as well as of others, must play
some important part in their economy. Of the five cases in which acids
did not cause the tentacles to be inflected, one is doubtful; for uric
acid did act slightly, and caused a copious secretion of mucus. Mere
sourness to the taste is no

* According to M. Fournier (‘De la Fcondation dans les Phanrogames.’
1863, p. 61) drops of acetic, hydrocyanic, and sulphuric acid cause the
stamens of Berberis instantly to close; though drops of water have no
such power, which latter statement I can confirm; [page 197]

criterion of the power of an acid on Drosera, as citric and tartaric
acids are very sour, yet do not excite inflection. It is remarkable how
acids differ in their power. Thus, hydrochloric acid acts far less
powerfully than hydriodic and many other acids of the same strength,
and is not poisonous. This is an interesting fact, as hydrochloric acid
plays so important a part in the digestive process of animals. Formic
acid induces very slight inflection, and is not poisonous; whereas its
ally, acetic acid, acts rapidly and powerfully, and is poisonous. Malic
acid acts slightly, whereas citric and tartaric acids produce no
effect. Lactic acid is poisonous, and is remarkable from inducing
inflection only after a considerable interval of time. Nothing
surprised me more than that a solution of benzoic acid, so weak as to
be hardly acidulous to the taste, should act with great rapidity and be
highly poisonous; for I am informed that it produces no marked effect
on the animal economy. It may be seen, by looking down the list at the
head of this discussion, that most of the acids are poisonous, often
highly so. Diluted acids are known to induce negative osmose,* and the
poisonous action of so many acids on Drosera is, perhaps, connected
with this power, for we have seen that the fluids in which they were
immersed often became pink, and the glands pale-coloured or white. Many
of the poisonous acids, such as hydriodic, benzoic, hippuric, and
carbolic (but I neglected to record all the cases), caused the
secretion of an extraordinary amount of mucus, so that long ropes of
this matter hung from the leaves when they were lifted out of the
solutions. Other acids, such as hydrochloric and malic, have no such
ten-

* Miller’s ‘Elements of Chemistry,’ part i. 1867, p. 87. [page 198]

dency; in these two latter cases the surrounding fluid was not coloured
pink, and the leaves were not poisoned. On the other hand, propionic
acid, which is poisonous, does not cause much mucus to be secreted, yet
the surrounding fluid became slightly pink. Lastly, as in the case of
saline solutions, leaves, after being immersed in certain acids, were
soon acted on by phosphate of ammonia; on the other hand, they were not
thus affected after immersion in certain other acids. To this subject,
however, I shall have to recur. [page 199]