The Determinative Action of Environic Factors Upon Neobeckir acquatica Greene. 279 
well as by a number of agencies to the action of wbich the plant is 
not ordinarily subject. Development may be incluced in which the 
series of leaves formed on successive internodes will retrogress from 
the mature terrestrial or aquatic form to the nepionic or juvenile type. 
Nearly all of the alterations noted in the series of foliar Organs 
were of a kind which yielded structures suitable for functionation and 
existence under the conditions which induced their formation. To this 
there is the exception of flattened leaf-divisions which are sometimes 
formed on aquatic leaves. The retrogressive series in which successive 
leaves were caused to vary from a mature aquatic or terrestrial type 
toward the juvenile or nepionic form is an example of an entirely 
different reaction. Here the influence of the transplantation or some 
external agency induces rejuvenation or the condition of the plasma 
characteristic of the earlier stages of ontogeny. One may imagine a 
bud with leaf-primordia in all stages of development toward the mature 
divided type eitlier of the aquatic or terrestrial form. The rejuvenated 
protoplasm now may be taken to be in a condition in which the diffe- 
rentiation necessary to the development of the adult form is made im- 
possible and consequently simple growth without such further differentiation 
ensues with the result that each leaf coines to its full size with an 
arrested development the youngest of the series having all of the 
characters of the nepionic type. A fair parallel is offered by the 
behavior of etiolated Organs in which growth without differentiation is 
very marked. 
Summary. 
The experiments through wich this plant have been carried 
include cultures as terrestrials and aquatics in a temperate house of 
the New York Botanical Garden, cultures in the soil in the open in 
the same place, cultures in a tropical climate at Cinchona in Jamaica 
(7,345 ft.) in the soil in the open, in the montane plantation of the 
Desert Laboratory in the Santa Catalina mountains in Arizona at 
8,000 ft., in the glass house of the Desert Laboratory 2,700 ft. in a 
sub-tropical climate with extreme temperatures, and in the garden of 
the Coastal Laboratory at Carmel, California, in a foggy cool, equable 
oceanic climate. Full development with the formation of flowers of this 
aquatic was secured at the last named place only. The plant however 
is seen to endure an extremely wide ränge of conditions, in which the 
diversity of its leaf structure may be a facto]' of importance. 
