344 



The Botanical Gazette. [December, 



the behavior of different plants in a saturated atmosphere is 

 by no means the same, but that there may be distinguished 



at least four types. 



(i) The rosette of radical leaves is loosened through 

 lengthening of internodal areas, both in darkness and satur- 



ated atmosphere. This is the case in Sempervivum tectorum. 



(2) There is no change of shape in obscurity or in a satu- 

 rated atmosphere. This is the case in Oxalis floribunda and 



Plantago media. 



(3) The plant undergoes dissociation of the radical rosette 

 in darkness but is unaffected by a saturated atmosphere. 

 This is the case in Taraxacum officinale. 



(4) The radical rosette is dissociated in the saturated at- 

 mosphere but is unaffected by obscurity. This is the case in 

 Capsella bursa-pastoris. 



Wiesner holds that in type I the internodal elongations are 

 in both cases due to increased transpiration. Type 2 he finds 

 difficult and calls into court that witness of last resort, hered- 

 ity, saying that there has been produced a phylogcnetischen 

 Entwicklung which can not be modified by changing conditions 

 in the life of a single culture plant. Type 3 is explained by 

 considering that light retards growth while transpiration has 

 little or no effect, and Type 4 indicates that transpiration may 

 be the condition of extended growth, while light has little 

 influence, or none at all. 



It does not seem at all certain that all of these explanations 

 are final. Type 2 could be better explained by some cause 

 separate from those investigated, acting either actively or 

 conservatively, to modify or inhibit the influence of the light 

 and transpiration current. The writer called attention in the 



Gazette of May, 1890, to a peculiar epinastic position of 



Solanum leaves under certain conditions which, he has since 

 come to believe were principally of modified transpiration. 

 This same plant was afterward examined by Vochting 4 and 

 very good photographs given of the peculiar epinastic posi- 

 tion. The Solanum plant also behaves in an interesting 

 manner in a saturated atmosphere, assuming much the ap- 

 pearance of an etiolated plant. This was recently determined 

 at the laboratories of the University of Minnesota. In a satu- 

 rated atmosphere the leaves, however, continue to be strongly 



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4 H. Vochting: Laubblaetter und Assimilationthatigkeit, Bot. Zeit., vol. 49. 

 no. 9. 



