The Do term illative Action of Eiivironic Factors Upon Nt^obeckiracquatica Greene, 279 



well as by a number of agencies to the action of which the plant is 

 not ordinarily subject Development may be indnceri in which the 

 series of leaves formed on successive intemodes 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 tlie 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 -prim ordia in all stages of development toward the mature 

 divided type either 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 comes to its full size with an 

 arrested development the youngest of tiie 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. 



Summaiy* 



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 bouse 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 range of conditions, in which the 

 diversity of its leaf structure may be a factor of importance. 



