258 HOW CROPS GROW. 



are fringed with a profusion of delicate hairs, and rapidly extend to a 

 length of from one to two inches. The lower ones, if they chance to 

 penetrate the water, become discolored and decay ; the others, however, 

 remain for a long time fresh, and of a white color. 



As already mentioned, Indian corn frequently produces 

 air-roots. The same is true of the oat, of buckwheat, of 

 the grape-vine, and of other plants of temperate re- 

 gions when they are placed for some time in tropical con- 

 ditions, i. e., when they grow in a rich soil and their over- 

 ground organs are surrounded by a very warm and very 

 moist atmosphere. 



It has been conjectured that these air-roots serve to ab- 

 sorb moisture from the air and thus aid to maintain the 

 growth of the plant. This subject has been studied by 

 linger, Chatin, and Duchartre. The observers first named 

 were led to conclude that these organs do absorb water 

 from the air. Duchartre, however, denies their absorptive 

 power. It is probably true that they can and do absorb 

 to some extent the water that exists as vapor in the at- 

 mosphere. At the same time they may not usually con- 

 dense enough to make good the loss that takes place in 

 other parts of the plant by evaporation. Hence the re- 

 sults of Duchartre, which were obtained on the entire 

 plant and not on the air-roots alone. (Elements de 

 J3otanigue, p. 216.) It certainly appears improbable that 

 organs which only develope themselves in a humid atmos- 

 phere, where the plant can have no lack of water, should 

 be specially charged with the office of collecting moisture 

 from the air. 



Root-Excretions. It has been supposed that the roots 

 of plants perform a function of excretion, the reverse of 

 absorption that plants, like animals, reject matters which 

 are no longer of use in their organism, and that the re- 

 jected matters are poisonous to the kind of vegetation 

 from which they originated. De Candolle, an eminent 

 French botanist, who first advanced this doctrine, founded 



