io8 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
conclusive evidence that simultaneity of flowering is at least in some plants 
determined by an external environmental factor. Two striking differences 
between the gregarious flowering of Dendrobium crumenatum and that of 
bamboos tend further to support this belief. In the bamboos flowering is 
rhythmic. In the orchid the periods between flowering dates vary from a 
few days to several months. There is no rhythmic periodicity here. 
The second striking difference between the gregarious flowering of 
orchids and that of bamboos is that in the latter case all the individuals of a 
bamboo forest are of the same age, while among an assemblage of orchids 
the individuals may be of quite different ages. Without further considera¬ 
tion one would be inclined to regard some external stimulus as the cause of 
the irregular gregarious flowering in the pigeon orchid. 
The writer has shown, in the article referred to (21), that simultaneity 
of flowering in Dendrobium crumenatum rests not upon a climatic but upon 
a heritable factor, namely, the innate disposition of the plants to develop 
all their flower buds to the same degree of advancement, at which point 
growth ceases. 6 The climatic factor arouses the buds—which are all of the 
same age and which, therefore, all require the same length of time (eight 
days) to complete development—to further activity, and thus determines 
merely the exact time of flowering and not the simultaneity of it. 
Conclusion 
As biological science progresses, many vital phenomena, which in the 
past have been regarded as resident wholly within the organism and in no 
way determined by the external environment, are one by one shown to be 
in many instances materially influenced, and in some instances directly 
determined, by environmental factors. While it must be admitted that 
one cannot altogether dissociate an organism from its environment, yet 
this hardly precludes one from regarding some vital phenomena as strictly 
innate. The origin of variations and mutations forces one, it seems to me, 
to admit the existence of at least a certain amount of independence of 
function of the germ plasm from its environment. 
The opposition of some biologists to the belief in a hereditary disposition 
of plants which is responsible for periodicity (in growth, reproduction, etc.) 
is apparently based on a fear of giving support to any hypothesis which 
would attribute to a plant self-regulation and would tend to dissociate the 
plant from its environment. But there is nothing mysterious in periodicity 
any more than in the radio-activity of certain metals or in the chemical 
reaction which takes place in a test tube regardless of the surrounding 
conditions. The causes are merely internal instead of external. 
Of the many vital phenomena which are rhythmic in plants—leaf 
production, leaf fall, cambium activity, reproduction, the synthesis and 
6 For a complete discussion of the possible mechanism involved see the article referred 
to (21). 
