248 INDIRECT BENEFITS DERIVED FROM INSECTS. 



The number of insects thus destroyed is prodigious. It is 

 scarcely possible to find a flower of the Muscicapce asclepiadecB 

 that has not entrapped its victim, and some of them in the 

 United States closely cover hundreds of acres together. 



What may be the precise use of this faculty is not so ap- 

 parent. Dr. Barton doubts whether the flowers that catch 

 insects, being only temporary organs, can derive any nutriment 

 from them ; and he does not think it probable that the leaves 

 of DioncBa, 8ic., 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 en- 

 snared 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, nurseryman in King's 

 Road, London, seems to prove that, in the case of Dion(Ba 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 whose leaves he laid fine filaments of 

 raw beef was much more luxuriant in its growth than others 

 not so treated.^ 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 CrahronidcB, which 

 dragged several large flies to the Sarracenia adunca, and 

 having with some diflSculty 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. ^ 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 



1 Elements of the Science of Botany, 62. 



2 Smith's Introduction to Botany, 195. 



