The Determinative Action of Environic Factors Upon 



Neobeclcia acquatica Greene ^>. 



By Dr. D. T. Mac Douflal 



(With 14 figures in test.) 



The march of development of the metameres in the ontogeny of 

 a large number of seed-plants is attended with the formation of a series 

 of foliar organs varying progressively through a wide range of form and 

 structure from the nepionic leaves to the flora! bracts. That these 

 leaf-characters are indicative of a complex of morphogenic and physiologic 

 characters essentially different, in the internodes which bear them, is 

 well evidenced by the fact that the rejuvenation phenomena and the 

 mature individuals which may follow propagation by metameres from 

 the earlier or later part of the series may be widely different- 

 One phase of this behavior is illustrated by the work of ShuU 

 with Sium in which it was shown definitely that the rejuvenescence 

 of a bud borne on any intemode was followed by the formation of 

 foliar organs the approximation of which to the true nepionic leaves 

 corresponded to the nearness of the intemode to the senescent or floral 

 end of the series. (ShuU, G. H., Stages in the Developiuent of Sium 

 cicutaefolium. Publ. Carnegie Inst of Wash. Nr. 30. 1905.) 



Still another phase of this matter is exhibited by plants in which 

 for example, propagation from juvenile individuals representing the 

 earlier part with the ontogenetic series results only in other juvenile 

 individuals which do not display characters included in adults in which 

 the entire progression to senescence has been followed. There is a 

 confluence of thought toward acceptance of the conclusion that all of 

 these facts must rest upon a definite physical basis of formative or 

 specialized material characteristic of the stages of development and with 



1) Diverse and changing usage has made necessary the citation, of this plant 

 also under the names of Nasturtium lacustre A. Gray, Roripa Americana 

 Britton and Uadicula aquatica (Eat.) Robinson, in correspondence with American 

 botanists during the ten years in which it has been under cultivation. 



