The Determinative Action of Environic Factors Upon 
Neobeckia acquatica Greene 1 ). 
By Dr. D. T. Mac Dougai 
(With 14 figures in text.) 
The marck 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 ränge of form and 
structure from the nepionic leaves to the floral bracts. That these 
leaf-ckaracters 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 rejnvenation 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 Shull 
with Sium in which it was shown definitely that the rejuvenescence 
of a bud borne on any internode was followed by the formation of 
foliar organs the approximation of which to the true nepionic leaves 
corresponded to the nearness of the internode to the senescent or floral 
end of the series. (Shull, G. H., Stages in the Development 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 Radicula aquatica (Eat.) Robinson, in correspondence with American 
botanists during the ten years in which it has been under cultivation. 
