94 PEOPAGATION" OF PLANTS. 



or find an abiding place either in the atmosphere or soil ; 

 for while one authority allows it free entrance to the 

 roots, another is equally certain that it only finds its way 

 into the plants through the leaves. In a recent work of 

 Dr. M. T. Masters, in speaking of root action, he says : 

 "No passage of aeid fluid out of the cell takes place, 

 root excretions having no existence," etc. But in another 

 paragraph on the same page he says : "On the other 

 hand, roots do not absorb carbonic acid gas nor exhale 

 oxygen as the leaves do (in the sunlight), but they do 

 give off carbonic acid gas, which, with the aid of water, 

 converts the insoluble carbonates of the soil into soluble 

 bicarbonates, and exercise a similar power of solution in 

 the case of phosphates." If the roots "do give off car- 

 bonic acid gas," it is certainly by an "excretive" action, 

 which the author utterly denies in the first paragraph 

 quoted. In describing the action and function of leaves 

 he says : " The paramount function of the leaf is the 

 absorption and assimilation of carbon. Carbon, as such, 

 does not exist in the atmosphere, unless, indeed, as an 

 impurity in the air of towns, and is a very prejudicial one 

 to plants. It is in the form of carbonic acid gas — a com- 

 bination of carbon and oxygen — that it is found in the 

 atmosphere, but only in small proportion compared with 

 the other constituents. In the plant, carbon exists in 

 much larger proportion than any other ingredient, with 

 the sole exception of water. It forms, in fact, fifty per 

 cent, of the dry matter of plants left behind after, the 

 water and gases have been expelled by heat. This large 

 quantity of carbon has to be taken up in the form of 

 carbonic acid hy the leaves." 



There can be no question in regard to the meaning of 

 Dr. Master's words, for they are direct and to the point 

 — namely, the carbon of plants is derived from the air 

 and through the leaves only, consequently from a source 

 where this important element is the least abundant, and. 



