292 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



lows: "The greatest divergences of reaction appear during the 

 second or unfolding stage. The leaves of some plants quickly perish 

 at the beginning of this stage if in an atmosphere free from carbon 

 dioxide ; others carry on a more or less complete development before 

 perishing; others attain a size somewhat less than the normal, and 

 then continue to live in an apparently healthy manner; and others 

 attain a normal size, and continue existence showing no deviation 

 from the normal." It was also demonstrated that the casting away 

 of useless or functionless organs was also a matter of morphological 

 constitution to some extent and that some species are not capable of 

 this adaptive reaction. '^'^ A similar state of affairs is to be predicated 

 of organs grown under etiolative conditions, and the form of the 

 plant when cultivated in darkness must be a result of the lack of 

 the specific morphogenetic influence of light and also of the lack of 

 functional activity of such organs ; although it is not to be taken 

 for granted that all leaves on all plants are functionless in dark- 

 ness. On the contrary the organization of the shoot is such, in 

 some instances, that the entire amount of transpiration is carried on 

 by the etiolated leaves, and the needs of respiration may also operate 

 to stimulate the development of the tissues to some extent. The 

 varying importance of what may be termed these minor functions 

 may be taken to account for the different degrees of development 

 and differentiation reached by various etiolative organs in darkness ; 

 and it is to these factors that at least a portion of the increased devel- 

 opment of the leaves and shoots when freed from the competition 

 and aid of concurrent organs in darkness must be ascribed. 



Some highly interesting considerations are raised by the results 

 of Bonnier in the culture of shrubs in continuous electrical illumina- 

 tion and by the experiments of Browne and Escombe (p. 274), in re- 

 gard to the size and development of leaves and internodes. The 

 development of leaves in atmospheres containing abnormally large 

 proportions of carbon dioxide, in which an increased photosynthesis 

 occurred, resulted in these organs attaining sizes below the average, 

 and also resulted in the formation of stems of about the usual length 

 but composed of a greater number of internodes than the normal, 

 which were, of course, shorter than the normal average. On the 

 other hand, the development of shrubs in continuous illumination of 



'"^MacDougal. Relation of the growth of leaves and the chlorophvl function. 

 Jour. Linn. Soc. London, 31 : 525-546. 1896. 



