108 AMERICAN JOURNAL OF BOTANY [Vol. 10, 



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 crumenatiim 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 crumenatiim 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). 



