94 AMERICAN JOURNAL OF BOTANY [Vol. 10, 



into a pine. We may even go further than this and maintain that the 

 spreading form of the common poplar {Populus nigra) and the tall slender 

 form of the Lombardy poplar (P. nigra var. italica) must, since the latter 

 arose as a mutation of the former and since both forms breed true in the 

 same environment, be due to the special nature of the protoplasm of the 

 two trees and not to environmental factors. Those who hold the extreme 

 view that "all characters are innate, acquired, germinal, somatic, and 

 inheritable in exactly the same sense and degree" (7, p. 596) will find some 

 difficulty in explaining the origin of fluctuations and mutations in certain 

 individuals of a species when other individuals of the same species in the 

 same environment remain true to type. 



That external environment plays an important if not an inseparable 

 part in inheritance and development is a fact of far-reaching significance. 

 The problem of the biologist is to determine to what extent the heritable 

 disposition of plants is susceptible to influence by the external environment. 



In a study of this sort one must guard against concluding that an en- 

 vironmental factor is the cause of a vital phenomenon because it has been 

 found to influence the phenomenon. Thus, from Garner and Allard's work 

 we may conclude that length of exposure to light determines the time of 

 flowering in certain plants, but we are not justified in regarding this environ- 

 mental factor as the cause of flowering. The act of attaining sexual maturity 

 is innate in all organisms, just as is senility. The exact point in the life 

 cycle at which the individual shall become sexually mature is in some plants 

 evidently sensible to external influence; i.e., it is capable of being shoved 

 this way or that by the environment. 



The problem of determining the environmental factors which influence 

 the flowering of plants assumes a special interest when considered in refer- 

 ence to those plants which flower only after a period of many years of 

 purely vegetative growth. Particularly interesting does the problem be- 

 come when applied to those plants in which all the individuals of a species 

 throughout a given region attain sexual maturity simultaneously. The 

 bamboos (many of them) belong to this category. 



Drought as a Cause of Gregarious Flowering 

 in Bamboos and Palms 



One of the oldest theories of the cause of gregarious flowering in bamboos 

 is that this simultaneous anthesis is occasioned by drought (18, p. 251). 

 This theory is still held by many biologists. Some (8, 16) have advanced 

 another hypothesis, namely, that periodic flowering in bamboos is the 

 result of a depletion of nourishment. Both theories are opposed to that 

 which would attribute this sex phenomenon to a heritable factor in the plant. 



The chief criticism to be directed against such theories is that their 

 supporters have failed to look further than the particular group of plants 

 and the special set of environmental factors under observation. 



