23 



tion. In any case their existence in leaves and shoots 

 means nothing as to conditions in roots or other sub- 

 terranean parts. It is true, however, that sir passages 

 which appear to be continuous with the subaerial aerating 

 system have been identified in a number of roots and are 

 usually imagined to function as channels of oxygen supply. 



There appears to have been no direct experimentation on 

 the function of these air passages in roots or on the 

 amount of oxygen which is, or can be, supplied to the 

 deep-lying roots in this way. In the search for evidence 

 implying the need of soil aeration the matter is not 

 important, since the possession of ai$ efficient internal 

 aerating system would, in itself, make a root reasonably 

 independent of the degree of aeration in the surrounding 

 soil. But in connection with the problem of the nature of 

 feise root respiration it is interesting to inquire what 

 quantity of oxygen could be supplied to roots by means 

 of these internal aerating systems. 



"T* Hohnfeldt,- Bot. Jahresber. 1880 : 48; 

 Kohl,- Transpiration der Pflanzen, p. 26, 1886; Bancroft, - 

 Bot. Jahresber. 1889 : 49; Devaux,- Bull. 3oc. Bot. 38: 

 48 (1891); Pfeffer,- Druck und Arbeitsleistung, p. 245 

 (1893); Brenner,- Ber. deut. bot. Ges._20: 175 (1902); 

 Warming,- Oecology, p. 44 (1909); Hunter,- Ann. Bot. 2y_: 

 627-634 (1914). 



