570 ANNUAL, JEtEPORT SMITHSONIAN INSTITUTION, 1920. 



propagation by seeds constitutes the sole method of perpetuating the 

 species. Indeed, the typical course of development of these plants 

 is such that it was formerly believed all other activities are merely 

 preliminary or incidental to the successful accomplishment of seed 

 development or sexual reproduction. This suggestion implies that 

 flowering and fruit formation simply express inherent properties 

 of the living protoplasm, without special intervention of the en- 

 vironment, provided only that conditions of temperature, moisture, 

 light, and soil reasonably favorable to plant growth are supplied. 

 The present-day plant physiologist, however, recognizes that the 

 plant merely inherits capacity to respond in definite and specific 

 manner to given conditions of its environment, rather than that de- 

 velopment must be along fixed lines in spite of differences in environ- 

 ment. Still, it must be admitted that until recently little was known 

 as to the factors of the environment which actually control flowering 

 and fruiting. 



In the light of the above-mentioned considerations one naturally 

 would be led to conclude that although the internal changes involved 

 in flower and fruit formation are very profound and complex in 

 character, these processes can not be regarded as proceeding in a 

 fixed course independently of environmental influences. It is appar- 

 ent that any satisfactory explanation of underlying causes and the 

 mechanism of the internal processes whereby the green shoot is 

 transformed into flower and fruit must take into account a number 

 of striking features of development which are associated with this 

 change in activity. Among these are the multiplicity of forms 

 evolved, the marked periodicity in occurrence of flowering and fruit- 

 ing in the individual species, but decided diversity in the annual 

 flowering seasons of different species, differences in time required 

 for reaching these stages of development in different species and 

 changes in the behavior of a particular species when transferred 

 northward or southward. It is the purpose of this article to 

 show that the relative length of day and night is an external factor 

 which may largely determine whether a given plant is able to flower 

 and develop fruit in any particular region and in any particular 

 season of the year, and that, consequently, the prevailing seasonal 

 length of day in any region may greatly influence the character of 

 its vegetation, barring, of course, the effects of special and purely 

 local conditions, such as absence of rainfall. 



PECULIAR BEHAVIOR OF CERTAIN VARIETIES OF SOY BEAN AND 

 TOBACCO WHEN GROWN AT DIFFERENT SEASONS OF THE YEAR. 



The soy bean {Soja max (L) Piper) is a leguminous summer 

 annual of great value as a farm crop for improving the soil, for the 

 production of food for live stock, and as a source of vegetable oil. 



