m. was as great, within a hair s breadth, as when the drops were first
placed on the leaf. From this experiment we learn that the motor
impulse can be transmitted to a distance of .22 of an inch (5.590 mm.)
in a transverse direction from the midrib to both margins; but it would
be safer to say .2 of an inch (5.08 mm.) as the drops spread a little
beyond the midrib. The incurvation thus caused lasted for an unusually
short time.
Experiment 14. Three drops of a solution of one part of carbonate of
ammonia to 218 of water (2 grs. to 1 oz.) were placed on the margin of
a leaf. These excited so much secretion that in 1 h. 22 m. all three
drops ran together; but although the leaf was observed for 24 hrs.,
there was no trace of inflection. We know that a rather strong solution
of this salt, though it does not injure the leaves of Drosera,
paralyses their power of movement, and I have no doubt, from the
following case, that this holds good with Pinguicula.
Experiment 15. A row of drops of a solution of one part of carbonate of
ammonia to 875 of water (1 gr. to 2 oz.) was placed on the margin of a
leaf. In 1 hr. there was apparently some slight incurvation, and this
was well-marked in 3 hrs. 30 m. After 24 hrs. the margin was almost
completely re-expanded.
Experiment 16. A row of large drops of a solution of one part of
phosphate of ammonia to 4375 of water (1 gr. to 10 oz.) was placed
along the margin of a leaf. No effect was produced, and after 8 hrs.
fresh drops were added along the same margin without the least effect.
We know that a solution of this [page 376] strength acts powerfully on
Drosera, and it is just possible that the solution was too strong. I
regret that I did not try a weaker solution.
Experiment 17. As the pressure from bits of glass causes incurvation, I
scratched the margins of two leaves for some minutes with a blunt
needle, but no effect was produced. The surface of a leaf beneath a
drop of a strong infusion of raw meat was also rubbed for 10. m. with
the end of a bristle, so as to imitate the struggles of a captured
insect; but this part of the margin did not bend sooner than the other
parts with undisturbed drops of the infusion.]
We learn from the foregoing experiments that the margins of the leaves
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