The Determinative Action of Environic Factors Upon Neobeckia acquatica Greene. 265 



respect to the various organs. (See Goebel, Organography of Plants, 

 Part I, pag- 45 and 145. 1900-) 



The fact that the structure of the leaves of any part of the series 

 is generally of an obvious suitability for activity under the seasonal 

 conditions in which they usually are formed has led many writers to 

 assign a directly determinative action to the environment. The coin- 

 cidence of amplitude of range in intensity of environic conditions and 

 of correlated diversity of structure, as exemplified by Bidens Beckii, 

 Cabomba, Ranunculus delphinifolius, Proserpinaca palustris, 

 Slum cicutaefolium, and of Neobeckia the subject of the study descri- 

 bed on the following pages, might be one of simple survival by fitness, or on 

 the other hand, fitness might in itself be induced by the agencies encountered. 



Any consideration of the matter raises the question at once as 

 to how far the various forms of a polymorphic series are morphologi- 



Fig. 1, Seedlings of Siiim cicutaefolium grown as terreBtrials. 



cally determinative, following an unmodifiable proceedure, and to what 

 extent the morphogeny of the metameres may be modified by raani- 

 pulation of the external conditions affecting their development. The 

 results of ShuU cited above seem to show that the ontogeny of Slum 

 is independent and that external conditions may be modified to increase 

 the range of variability or to cause rejuvenescence at any st^ge, yet 

 their influence goes no farther. 



This variation may be illustrated by some results which the author 

 obtained with Sium, in the New York Botanical Garden in 1903- Two 

 series of germinating seeds in soil were made- One was treated in 

 the ordinary manner and the other was submerged to a depth of 10 cm 

 in water. 



The seedlings germinated as terrestrials grew more rapidly than 

 those under water and had a main root 2 to 3 cm long with a few 

 lateral branches, and had also some adventitions roots arising from the 



