TISSUES AND SIMPLE ORGANS. 



149 



and similar phenomena we shall add anotlier which has been ob- 

 served in about fifteen species of plants, that is, the digestion of 

 animal substance by plants. The most interesting features of these 

 *' insectivorous " plants are the specific arrangements for the cap- 

 ture of living insects. 



Our indigenous genus Drosera shall first be cited as a typical 

 example (Fig. 90). Small insects adhere to the sticky substance 

 excreted from the glandular en- 

 largements of the "tentacles" 

 (trichomes) covering the margin 

 and the entire upper surface of 

 the leaf. The pressure of the 

 insect acts as a stimulus M'hieh is 

 conveyed from tentacle to ten- 

 tacle, until finally all the tentacles 

 incline toward the middle of the 

 leaf (Fig. 90, e). The insect dies 

 and the albuminoid portion is dis- 

 solved by a coj)ious secretion from 

 the many-celled glandular struc- 

 tures which acts similar to the 

 gastric ferment pepsin.' The 

 chitinous skeleton remains un- 

 changed and is finally discarded. 

 The dissolved substances are 

 taken up by the leaf, and the 

 trichomes resume their normal ir- 

 ritable position. In Dionaea 

 the glandular hairs secrete the 

 ferment and the acid only after they have been irritated. In the 

 leaves of NepentJnis (Madagascar) the ferment is secreted without 

 any mechanical stinuilus, while the secretion of acid is due to the 

 presence of a chemical stinuilus. In the case of Drosera it remains 

 a question whether or not the ferment is secreted without the 

 presence of a stimulus. It is believed that the appropriation of 

 animal food by some insectivorous plants {Dionaea and Aldrovanda) 



Fig. 90. — Drosera. 

 (After Krass and Landois.) 



' According to recent investigations tbis digestive ferment is secreted by bac- 

 teria living on the plant. — Trans. 



