INDIRECT BENEFITS DERIVED FROM INSECTS. 291 



any nutriment from them ; and he does not think it pro- 

 bable that the leaves of Dionaea, &c, which are usually 

 found in rich boggy soil, can have any need of additional 

 stimulus. As nothing however 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 expe- 

 riment of Mr. Knight's, nurseryman in King's Road, 

 London, seems to prove that in the case of Dionaea, at 

 least, the very end in view, contrary to Dr. Barton's sup- 

 position, is the supplying the leaves with animal manure ; 

 for he found that a plant upon whose leaves he laid fine 

 filaments of raw beef, was much more luxuriant in its 

 growth than others not so treated a . 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 ve- 

 getation. 



Most of the insects which are found in the tubular 

 leaves of this and similar plants enter into them volun- 

 tarily ; 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 Sphegiadce (SpJiex, L.), which dragged several 

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

 difficulty forced them under the lid or cover of its leaf, de- 

 posited them in its tubular part which was half filled with 

 water: and on examination all the leaves were found 



a Elements of the Science of Botany, 62. 

 u 2 



