376 PINGUICULA VULGARIS. Cuar. XVI 
strength acts pc werfully on Drosera, and it is just possible that 
tha solution was too strong. I regret that Idid not try a weaker 
solution. 
Experi.nent 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 curl inwards when excited by 
the mere pressure of objects not yielding any soluble 
matter, by objects yielding such matter, and by some 
fluids—namely an infusion of raw meat and a weak 
solution of carbonate of ammonia. A stronger solu- 
tion of two grains of this salt to an ounce of water, 
though exciting copious secretion, -paralyses the leaf. 
Drops of water and of a solution of sugar or gum did not 
cause any movement. Scratching the surface of the 
leaf for some minutes produced no effect. Therefore, 
as far as we at present know, only two causes—namely 
slight conttnued pressure and the absorption of nitro- 
genous matter—excite movement. It is only the 
margins of the leaf which bend, for the apex never 
curves towards the base. The pedicels of the glan- 
dular hairs have no power of movement. I observed 
on several occasions that the surface of the leaf be- 
came slightly concave where bits of meat or large 
flies had long lain, but this may have been due to 
injury from over-stimulation. 
The shortest time in which plainly marked move- 
ment was observed was 2 hrs. 17 m., and this occurred 
when either nitrogenous substances or fluids were 
placed on the leaves; but I believe that in some cases 
