168 INDIRECT BENEFITS DERIVED FROM INSECTS. 



What may be the precise use of this faculty is not so apparent. Dr. 

 Barton doubts whether the flowers that catch insects, being only tempo- 

 rary organs, can derive any nutriment from them ; and he does not think it 

 probable that the leaves of Dioncea, &c., which are usually found in rich 

 boggy soil, can have any need of additional stimulus. As nothing, how- 

 ever, is made in vain, there can be little doubt that these ensnared insects 

 are subservient to some important purpose in the economy of the plants 

 which are endowed with the faculty of taking them, though we may be 

 ignorant what that purpose is ; and an experiment of Mr. Knight's, nur- 

 seryman in King's Road, London, seems to prove that, in the case of 

 Dioncsa at least, the very end in view, contrary to Dr. Barton's supposi- 

 tion, is the supplying the leaves with animal manure ; for he found that 

 a plant upon \yhose leaves he laid fine filaments of raw beef was much 

 more luxuriant in its growth than others not so treated. 1 Possibly the 

 air evolved from the putrefying insects with which Sarracenia purpurea is 

 sometimes so filled as to scent the atmosphere round it, may be in a similar 

 manner favourable to its vegetation. 



Most of the insects which are found in the tubular leaves of this and 

 similar plants enter into them voluntarily ; but Sir James Smith mentions 

 a curious fact, from which it appears that in some cases they are deposited 

 by other species. One of the gardeners of the Liverpool Botanic Garden 

 observed an insect, from the description one of the Crabronidce, which 

 dragged several large flies to the Sarracenia adunca, and having with some 

 difficulty forced them under the lid or cover of its leaf, deposited them in 

 its tubular part, which was half filled with water ; and on examination all 

 the .leaves were found crowded with dead or drowning flies. 2 What was 

 the object of this singular manoeuvre does not seem very obvious. At the 

 first glance one might suppose that, having deposited an egg in the fly, it 

 intended to avail itself of the tube of the leaf instead of a burrow. "Yet 

 we know of no such strange deviation from natural instinct, which would 

 be the more remarkable, because the insect was European, while the plant 

 was American, and growing in a hot-house. And, at any rate it does not 

 seem very likely that the insect would commit her egg to the tube without 

 having previously examined it ; in which case she must have discovered it 

 to be half full of water, and consequently unfit for her purpose. It is not 

 so wonderful that many large flies should, as Professor Barton informs us, 

 drop their eggs into the Ascidia furnished with dead carcasses ; and it 

 seems very probable that Dytisci oviposit in them ; for the Squilla, which 

 Rumphius found there, was probably one of their larvae, this being the 

 old name for them. 8 



However problematical the agency of insects caught by plants as to their 

 nutriment, there can be no doubt that many species perform an important 

 function with regard to their impregnation, which indeed without their aid 

 would in some cases never take place at all. Thus, for the due fertilisation of 

 the common Barberry (Berberis vulgaris), it is necessary that the irritable 

 stamens should be brought into contact with the pistil by the application 

 of some stimulus to the base of the filament ; but this would never take 

 place were not insects attracted by the melliferous glands of the flower to 



1 Elements of the Science of Botany, 62. 

 8 Smith's Introduction to Botany, 195 

 Mouffet, 319. 



