94 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
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. 
