Cuap. I. ACTION OF THE PARTS. 17 
assuredly have been carried to the centre of the leaf 
and been securely clasped on all sides. We shall 
hereafter see what excessively small doses of certain 
organic fluids and saline solutions cause strongly 
marked inflection. 
Whether insects alight on the leaves by mere 
chance, as a resting-place, or are attracted by the 
odour of the secretion, I know not. I suspect from 
the number of insects caught by the English species 
of Drosera, and from what I have observed with some 
exotic species kept in my greenhouse, that the odour 
is attractive. In this latter case the leaves may be 
compared with a baited trap; in the former case with 
a trap laid in a run frequented by game, but without 
any bait. 
That the glands possess the power of absorption, is 
shown by their almost instantaneously becoming dark- 
coloured when given a minute quantity of carbonate of 
ammonia ; the change of colour being chiefly or exclu- 
sively due to the rapid aggregation of their contents. 
When certain other fluids are added, they become pale- 
coloured. Their power of absorption is, however, best 
shown by the widely different results which follow, 
from placing drops of various nitrogenous and non- 
nitrogenous fluids of the same density on the glands 
of the disc, or on a single marginal gland; and like- 
wise by the very different lengths of time during which 
the tentacles remain inflected over objects, which yield 
or do not yield soluble nitrogenous matter. This 
same conclusion might indeed have been inferred from 
the structure and movements of the leaves, which are 
so admirably adapted for capturing insects. 
The absorption of animal matter from captured 
insects explains how Drosera can flourish in extremely 
poor peaty soil,—in some cases where nothing but 
