NUTRITION 83 



gen compounds, largely proteids and insoluble, is followed 

 by the secretion from the glandular ends of the hairs of a 

 peptonizing enzym which attacks the nutritious substances 

 and dissolves them. These solutions are absorbed into the 

 plant through the cells secreting the enzym, diffuse from 

 them into other cells, and are conducted away by the vas- 

 cular bundle. After all the nutritious substances in the 

 captured insect have been digested (dissolved) and ab- 

 sorbed, the leaf unrolls, again becomes flat, the tentacles 

 loose their hold and become straight, the chitinous shell 

 and the other useless remnants are exposed, dry. and blow 

 away. The leaf is now ready to capture another insect. It 

 is reported that each leaf has a digestive capacity for two 

 or three flies. 



When Drosera is able, by capturing and digesting insects, 

 to supplement the nitrogenous food which it, like other 

 plants, elaborates from the nitrates absorbed from the soil 

 and the sugars made in its own leaves, it attains a larger 

 size and produces more and better seeds ( other things being 

 equal) than when it must depend solely upon the complex 

 nitrogenous foods made by itself. 



It has been claimed by Tischutkin, * and the view has been 

 somewhat generally accepted without due investigation, 

 that the peptonizing enzym is secreted mainly, if not wholly, 

 by bacteria symbiotically associated with Drosera on its 

 tentacles, and not by the gland cells of the tentacles. There 

 can be no question of the constant presence, under natural 

 conditions, of bacteria on the tentacles, and it would be re- 

 markable if there were none among these which formed a 

 peptonizing enzym. However, these bacteria, peptonizing 

 and other, are no more symbiotically associated with Dro- 

 sera and no more concerned in the digestion of its insect 

 food than the bacteria of the human mouth and digestive 

 tract are symbiotically associated with man and aid in his 

 digestive processes. In both cases we have to do with bac- 

 teria unavoidably and constantly, but also accidentally and 



* Tischutkin N. A Russian paper reviewed in Botan. Centralblatt 

 Bd. 50. p. 304-j-. 1892 ; also a later paper reviewed in Botan. Central- 

 blatt Bd. 53. p. 322. 1893. 





