THE SUNDEWS 269 



or separately. The contact of indifferent solid bodies of 

 extremely small weight, such as splinters of glass, induces 

 a movement. Drops of water, even if they strike the 

 tentacles with considerable force, have no effect. The 

 stimulus is perceived by the head only of the tentacle, and 

 the reaction, due to a differential growth rate, takes place at 

 the base of the stalk ; a conduction of the excitation occurs. 

 Very small quantities of such nitrogenous compounds as 

 ammonium sulphate or white of egg produce the same 

 result ; less than one-thousandth of a milligram of 

 ammonium sulphate is effective. If the central tentacles 

 are stimulated they do not respond by movement, but they 

 do perceive the stimulus and transmit it to the marginal 

 tentacles, which then bend inwards. The stimulus is not 

 transmitted from one marginal tentacle to the others. 



The increased secretion, which is accompanied by a 

 change in the vacuoles of the cells, is also a result of the 

 stimulation, contact here being less powerful than chemical 

 action. The nature of the secretion, too, is altered ; it 

 contains an enzyme like pepsin and an acid. The enzyme 

 is capable of digesting proteins in an acid medium, breaking 

 them down, as has been shown by White (1910), to peptone, 

 which is then resorbed by the leaf cells. 



After the closing in of the tentacles upon the insect the 

 process of digestion goes on and may take several days, 

 depending on the size of the booty. When it is complete 

 the tentacles slowly fold back, and the fully opened leaf is 

 capable of capturing and digesting fresh prey. 



The process is similar in all the species of Drosera. 

 Some of the sub-tropical species are much larger than our 

 native sundews and have very different leaf forms. In 

 D. capensis the leaves are very long and narrow ; in Z). hinata 

 they are long and forked. In long-leaved types the move- 

 ment of the leaf blade may be extensive ; it may double up 

 or twist round the captured insect. In Drosophyllum 

 lusitanicum, a small Portuguese shrub, we meet a less active 

 condition. The leaves are long and narrow, and a single 

 one may catch dozens or even hundreds of little flies. 



