378 



THE FOOD OF PLANTS 



a great part in the reciprocal relationships of plants and insects. Equally 

 remarkable purposeful adaptations are exhibited among carnivorous fungi 1 , 



FIG. 56. Pitcher of Neptnthes, drawn 

 to smaller scale. 



FIG. 57. Leaves of Dionaea ntuscifxila. (A) opened, on each 

 leaf-segment the three irritable hairs may be seen. (B) an earwig is 

 captured between the closed leaf-segments. 



while freely motile plants seek out their prey as an animal does, and are 

 frequently attracted to their food by chemotactic stimulation. 



In Dionaca the absorption of the products 

 of digestion by the leaf causes it to wither and 

 die, and certain changes 2 usually occur in the 

 absorbing glands during digestion. In this way 

 an amount of peptone may be obtained which 

 forms a considerable fraction of the total amount 

 required, for frequently a large number of small 

 insects may be digested, while in the pitchers 

 of Nepenthes large insects may be captured 3 . 

 This carnivorous habit is probably solely for 

 the purpose of obtaining peptone, for sufficient 

 carbon dioxide is assimilated for all requirements. 

 It appears, however, that a supply of organic 

 nitrogen compounds is not an absolute neces- 

 sity to such plants, although it exercises an 

 extremely favourable influence upon growth and 



development, as it does also in the case of many fungi. Schenk was able to 

 cultivate Aldrovanda vesiculosa for two years on inorganic nutrient solutions ; 



FIG. 58. Leaf of Drosera rotuttdt- 

 Dula* 

 have 



folia (magnified). Owing to stimula 

 tion the hairs on the left side 



curved inwards. 



1 Zopf (Nova Acta d. Leopold. Akad., 1888, Bd. LIT, p. 331) mentions a fungus which captures 

 Nematodes. 



8 Cf. de Vries, Bot. Zeitnng, 1886, p. I ; Goebel, I.e., pp. 170, 198 ; also the literature quoted 

 in Sects, n and 16, on precipitation and aggregation. 



* Goebel, 1. c., p. 191 ; Haberlandt, Botanische Tropenreise, 1893, p. 58. 



