48 THE AMERICAN MONTHLY [Feb., 



Sachs however in his extended investigations, came to 

 the conclusion that tlie stomates are the principal agents 

 in the exchange of gases. The tendency of recent inves- 

 tigations is toward the establishment of the idea that ex- 

 change of gases takes place between the internal air cham- 

 bers in the plant and the surrounding air both by effu- 

 sion through the stomates, lenticels etc., and also by dif- 

 fusion of gases through the cell-walls even when they 

 are cutinized. 



The air-spaces in the body of the plant then are enti- 

 tled to much more attention than has been accorded them 

 by investigators. 



In submerged plants and plant parts, the abundance 

 and large size of intercellular spaces has long been known. 

 They are abundant and of large size in the roots of the 

 plant in question. They are especially abundant in the 

 aero tropic roots which are produced in autumn in such 

 abundance. They form longitudinal channels through 

 them and into these channels the external air finds access 

 by diffusion. 



A condensed statement of the conclusions reached, (the 

 details of the work may be found in the Proceedings of 

 the Am. Micro. Soc. for 1893) is as follows : 



The internal structure of the roots is characteristic of 

 the structure of submerged organs of aquatic plants, as 

 set forth by M. Constantin. (Ann. sc. nat. XIX Bot. p. 

 287, 1884.) The reduction of the xylem and the increase 

 in capacity of intercellular spaces, are conspicuous fea- 

 tures in the submerged organs. 



When grown in the garden for a period of years the 

 organs tend to develope a more perfect xylem and at the 

 same time reduce the size of the intercellular spaces. 



Gases may pass from one compartment to another by 

 effusion as Well as diffusion. The connecting openings 

 between spaces are not as conspicuous in the root of Mi- 

 fcariia as they are in the organs of some other species. 



