NUTRITION 85 



and absorbers of the unused products of these micro-organ- 

 isms. It would seem much more probable that, under their 

 normal conditions, the walls of these pitchers, as of the 

 Nepenthes, secrete an enzym which digests the bodies of en- 

 trapped insects. If this be true, the bacteria inevitably 

 present do not aid the plant, they simply rob it of food which 

 it can itself digest and afterwards absorb and assimilate. 



Most of the Utricularias are aquatics, the peculiar sub- 

 merged leaves of which entrap small crustaceans. It is still 

 undetermined whether the crustaceans are killed and di- 

 gested,* or whether they live on indefinitely. When they die 

 naturally their bodies become decomposed by the water 

 bacteria invariably present in the bladder-like leaves. At all 

 events, the excreta, containing considerable quantities of 

 organic nitrogenous matter, cannot fail to be directly or 

 indirectly useful to the plant which harbors the animals 

 producing them. The excreta may contain immediately 

 available substances ; the more refractory may first undergo 

 chemical transformation by water-bacteria ; finally the dead 

 bodies and the lifeless excreta, falling a prey to bacterial 

 activity, become available to the Utricularin, which profits 

 accordingly^ 



PARASITES 



A considerable number of plants of the most diverse sorts, 

 from the simplest to the most highly developed, are able to 

 live actively only upon or in the living bodies of other or- 

 ganisms. Thej^ may be able to survive in the resting condi- 

 tion entirely independently, but in this regard their seeds, 

 spores, and cysts are like all others. For active vegetation 

 they need their proper hosts. The relation of the parasite 

 to the host is not in all cases simply that of the fed to the 

 living organism which nourishes it. The host may do much 

 more than supply the parasite with food : it may give it 

 mechanical support, it may stimulate it to grow in charac- 

 teristic forms, it may assist in the dissemination of its off- 

 spring, it may protect it in a variety of ways. In all of 

 these respects tlie parasite is benefited. 



* Goebel K. L. r. p. 173. 



