CHAP. 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 



