46 Dr. J. C. Draper on Growth or 



commonly held as regards plants. Yet we propose to sliow that 

 in these organisms, as in animals, growth, as applied to evolu- 

 tion of structure or organization of material provided, is inse- 

 parably connected with oxidation. 



The discussion of the proposition in question necessarily 

 involves a preliminary review of the character of the gases ex- 

 haled from various plants. Commencing with the lower orga- 

 nisms, as Fungi, the uniform testimony is that these plants at 

 all times expire carbonic acid, while it is chiefly in the higher 

 plants, and especially in those which contain chlorophyl or 

 green colouring-matter, that carbonic acid is absorbed and oxy- 

 gen exhaled. The inquiry, then, in reality nan-ows itself down 

 to the examination of the growth of chlorophyl-bearing plants. 



Regarding these plants the statement is made and received 

 that tliey change their action according as they are examined 

 in the light or in the dark, exhaling oxygen under the first con- 

 dition, and carbonic acid under the second. Various explana- 

 tions of this change of action have been given, that generally 

 accepted accounting for it on the hypothesis of the absoi-ption 

 of carbonic acid by the roots, and its exhalation by the leaves 

 when light is no longer present. 



The change, on the contrary, appears to arise out of the 

 fact that two essentially different operations have been con- 

 founded, viz. the actual growth or evolution of structures in the 

 plant, and the decomposition of carbonic acid by the leaves 

 under the influence of the light, to provide the gum or other 

 materials that are to be organized. These two factors are 

 separated by Prof. J. W. Draper in his discussion of the con- 

 ditions of growth in plants. We propose to show that, by 

 adopting this proposition of two distinct operations in the higher 

 plants, all the apparent discrepancies regarding the growth of 

 these plants are explained. 



The growth of seedlings in the dark offering conditions in 

 which the act of groAvth or evolution of structure is accom- 

 plished without the collateral decomposition of carbonic acid, 

 I arranged two series of experiments in which growth under 

 this condition might be studied and compared with a similar 

 growth in the light. That the experiments might continue 

 over a sufficient period of time to furnish reliable comparative 

 results, I selected peas as the subject of trial, since these seeds 

 contain sufficient material to support the growth of seedlings 

 for a couple of weeks. 



To secure as far as possible uniformity of conditions between 

 the dark and light series, and also to facilitate the separation, 

 cleansing, and weighing of the roots, each pea was planted in a 

 glass cylinder, 1 inch in diameter and 6 inches long. These 



