Sundews 161 
all the other tentacles. It is not merely irritation 
that is thus communicated by one tentacle to another, 
but the knowledge of the direction whence the irrita- 
tion proceeded. This is shown by the fact that the 
tentacles so apprised bend over towards the centre 
of disturbance. 
It might be supposed that in so sensitive an 
instrument as the Sundew leaf must be, with its 
many tentacles, there would be a_ considerable 
amount of wasted effort owing to irritation being 
accidentally set up by grains of sand, drops of rain, 
ete., falling on the leaves; but this is not so. Itis 
remarkable that so fine a sense is possessed by the 
glands that they refuse to take notice of any inorganic 
solids. Place a gravel-fragment upon the leaf, and 
the tentacles will take little notice of its presence; 
but if the foreign substance be the merest fragment 
of hair, not only will the base of the tentacles be 
inflexed towards it, but the fluid exuding from the 
gland becomes acid and of a digestive quality. This 
is accompanied by changes in the substance of the 
oland of the tentacle itself—the purplish colouring 
matter being gathered up into little masses suspended 
in a colourless fluid. When the excitement has ceased 
and the tentacles have resumed their normal position, 
it is found that this colouring matter has been again 
dissolved, and now gives its colour to the whole of the 
internal fluid. In Mr. Darwin’s famous experiments on 
this plant he found a degree of sensitiveness greater 
probably than that possessed by any nerve in the human 
body, even when inflamed. A tiny morsel of cotton 
which weighed no more than ;,4,th part of a grain was 
S000 
sufficient vegetable matter to cause the tentacles to 
