14 DROSERA ROTUNDIFOLIA. [Chap. I. 



to curve inwards, though not a single gland had as yet 

 touched the body of the insect. Had I not interfered, this 

 minute gnat would assuredly have been carried to the cen- 

 tre 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 in- 

 flection. 



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 exclusively due to the rapid aggre- 

 gation of their contents. When certain other fluids are add- 

 ed, 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 likewise by the very 

 different lengths of time during which the tentacles remain 

 inflected over objects, which yield or do not yield soluble ni- 

 trogenous 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 sphagnum moss grows, 

 and mosses depend altogether on the atmosphere for their 

 nourishment. Although the leaves at a hasty glance do not 

 appear green, owing to the purple colour of the tentacles, yet 

 the upper and lower surfaces of the blade, the pedicels of the 

 central tentacles, and the petioles contain chlorophyll, so that, 

 no doubt, the plant obtains and assimilates carbonic acid 

 from the air. Nevertheless, considering the nature of the 

 soil where it grows, the supply of nitrogen would be extremely 



