[Reprinted from the American Journal of Botany, X: 93-112, February 1923.] 



LIBRARY 

 NEW YO*K 

 BOTANICAL 



OBSERVATIONS ON TT^'^AUSES OF GREGARIOUS 

 FLOWERING IN PLANTS 1 



William Seifriz 



(Received for publication May II, 1922) 



One of the most interesting and fundamental of biological problems is 

 that of the extent to which the life processes of an organism are influenced 

 by the external environment. In the past, biologists have been quite 

 content to rest secure in the belief that the most deep-seated characters in 

 organisms are developed in the individual and transmitted from one genera- 

 tion to another little influenced, and certainly not determined, by the ex- 

 ternal environment of the organism. That so fundamental a character as 

 paired eyes in vertebrates could in any great degree be influenced by a 

 change in external environment was hardly conceivable until Stockard 

 showed that if the eggs of the fish Fundulus are placed in sea water to which 

 a little magnesium chloride has been added they develop into embryos 

 with one medium cyclopean eye. 



Equally interesting to the botanist have been the experiments of Garner 

 and Allard (6), who were able by controlling the time of exposure of a 

 plant to light greatly to lower or increase the age at which the plant reaches 

 sexual maturity. Thus, the field aster, which commonly requires four 

 months (May to September) to reach sexual maturity, was made, by 

 decreasing the time of exposure to daylight, to bear flowers within a month 

 after germination (by June 18). Still more remarkable is the fact that 

 these same plants, instead of completing their life cycle by dying after 

 flowering, as they would have done in the field, developed new axillary 

 branches (on being restored to normal light exposure) and flowered a second 

 time in September. 



It is thus evident that certain characters of a deep-seated and fundamental 

 nature which heretofore have been regarded as immutable, are relatively 

 unstable and respond readily to changes in the external environment. It 

 is, consequently, not surprising that some biologists hold that all "characters 

 are of the nature of responses to environment" (7, p. 530), and that "every 

 life process must to some degree be dependent upon the external world" 

 (15, p. 285). 



While it is difficult to deny the truth of these statements in the face of 

 the remarkable experiments which have been performed, yet one wonders 

 how far such a theory will carry us. We hesitate to admit that the external 

 environment is in any way responsible for the fact that a pine seed develops 



1 Contribution from the Osborn Botanical Laboratory. 



93 



