556 Journal of Agricultural Research voi. xvm. no. n 



blossoming period is induced by the short length of day prevailing in 

 the early spring months. 



In a few words, previous work on light action clearly indicates that 

 permanent exclusion of light effectually prevents completion of the 

 blossoming and seed-forming processes, while in certain cases lengthening 

 the normal daily period of illumination by the use of artificial light or 

 by propagation in far northern latitudes hastens the approach of the 

 blossoming period, and, in the case of two species, shortening the daily ex- 

 posure to light induces the formation of precocious blossoms. That the 

 relative length of the day is really a dominating factor in plant reproduc- 

 tion processes, as is demonstrated in the present paper, seems not to have 

 been suspected by previous workers in this field. 



PRELIMINARY OBSERVATIONS 



In 1906 there were observed in a strain of Maryland Narrowleaf 

 tobacco {Nicotiana tabacum, L.)> w'hich is a very old variety, several 

 plants which grew to an extraordinary height and produced an abnormally 

 large number of leaves. As these plants showed no signs of blossoming 

 with the advent of cold weather, some of them were transplanted from 

 the field to the greenhouse and the stalks of others were cut off and the 

 stumps replanted in the greenhouse. These roots soon developed new 

 shoots which blossomed and produced seed, as did also the plants which 

 had been transferred in their entirety. This very interesting giant 

 tobacco, commonly known as Maryland Mammoth, which normally con- 

 tinues to grow till cold weather in the latitude of Washington, D. C, with- 

 out blossoming, proved to be a very valuable new type for commercial 

 purposes, but the above-mentioned procedure has been the only method 

 by which seed could be obtained. The type bred true from the outset, 

 and no matter how small the seed plant the progeny have always shown 

 the giant type of growth when propagated under favorable summer con- 

 ditions. It may be remarked at this point that inheritance of gigantism * 

 in this tobacco has been studied by one of the present writers (2) and 

 it has been shown that this character acts as a simple Mendelian recessive. 



On one occasion it was observed that seedlings of the Mammoth trans- 

 planted to 8-inch pots in late winter blossomed in early spring after reach- 

 ing a height of some 3 feet and developed an excellent crop of seed. 

 From this it was at first concluded that growing the plant under conditions 

 of partial starvation would induce blossoming, but this idea proved to be 

 erroneous. Repeated attempts during the summer months to force 

 blossoming by subjecting the plant to conditions which would permit 

 only limited growth were futile. On the other hand, it was found that 



• Throughout this paper the term gigantism is used to signify a tendency toward more or less indefinite 

 vegetative activity manifested by plants under certain favorable environmental conditions. Though an 

 inherited characteristic, it may come into expression only under definite conditions of environment; and 

 the present investigation seems to make it clear that the length of the daily light exposure is the controlling 

 factor. 



