344 ASSIMILATION. 



900. Canby 1 states that he has known "vigorous leaves to 

 devour their prey several times ; but ordinarily twice, or quite 

 often once, was enough to render them unserviceable." Mrs. 

 Treat 1 observes that " several leaves caught successively three 

 insects each, but most of them were not able to digest the third 

 fly, but died in the attempt. Five leaves, however, digested 

 each three flies and closed over the fourth, but died soon after 

 the fourth capture. Man}' leaves did not digest even one large 



insect." 



901. The following experiments by Darwin illustrate the flow 

 of the secretion: <k A bit of albumin ^ of an inch square but 

 only gV m thickness, and a piece of gelatin J inch long and T 1 ^ 

 broad, were placed on a leaf which eight days afterwards was 

 cut open. The surface was bathed with slightly adhesive acid 

 secretion, and the glands were all in an aggregated condition. 

 Not a vestige of the albumin or gelatin was left. Similarly 

 sized pieces were placed, at the same time, on wet moss in the 

 same pot, so as to be subjected to nearly similar conditions ; 

 after eight days these were brown, decayed, and matted with 

 fibres of mould, but had not disappeared." * 



902. That the digested matters are absorbed b}* the leaf has 

 been shown by the spectroscope, as in the case of Drosera ; but 

 no experiments are } r et on record as to the effect of this nutritive 

 matter on the plant. 



The character of the movement by which the trap is sprung is 

 spoken of in the chapter on " Movements." 3 



903. Other insect-catching Droseraceae. Drosera and Dionaea 

 are members of the order Droseraceae. Its four remaining 

 genera have also the power of capturing insects. 



Aldrovanda has been well called a miniature Dionaea. Its 

 bilobed leaves float in water (the plant being destitute of roots) . 

 Each leaf is two-valved, something after the fashion of Dionaea, 

 but each valve is made up of two parts. One, near the hinge 

 in the median line, is provided with colorless glands ; the 

 other, a sort of thin film outside, has no true glands. On 

 the inner part there are some extremely delicate hairs which 



1 Cited by Darwin : Insectivorous Plants, 1875, p. 311. 



2 Insectivorous Plants, p. 302. 



3 Burdon Sanderson has investigated the electrical disturbance which takes 

 place when the trap of Diona3a is sprung. For details and conclusions see the 

 following papers : Proceedings of the Royal Society, vol. xxi. p. 495, and Na- 

 ture, x., 1874, pp. 105, 127. But similar electrical disturbances are exhibited 

 when any fresh vegetable structure is sharply bent. 



