Mar. 1. 1920 Effect of Length of Day on Plant Growth 557 



seedlings grown in the greenhouse during the winter months invariably 

 blossomed without regard to the size of the pot containing the seedling or 

 the extent to which the plant was stunted by unfavorable nutrition con- 

 ditions. The seedlings behaved, therefore, like the summer-grown giant 

 plants which were transferred to the greenhouse late in the fall. Finally, 

 it was observed that the shoots which were constantly developing from 

 the transplanted roots of giant plants transferred to the greenhouse 

 blossomed freely during the winter months, but as early spring advanced 

 blossoming soon ceased and the younger shoots once more developed 

 giant stalks. Obviously, then, the time of year in which the Mammoth 

 tobacco develops determines whether the growth is of the giant character. 

 During the summer months the plants may attain a height of 10 to 15 feet 

 or more and produce many times the normal number of leaves without 

 blossoming, while during the winter months blossoming invariably occurs 

 before the plants attain a height of 5 feet. Naturally it became of interest 

 from both a practical and a scientific standpoint to determine the factor 

 of the environment responsible for the remarkable winter effect in forcing 

 blossoming. It may be added just here that gigantism also has been 

 observed in several distinct varieties of tobacco other than the Mary- 

 land — namely, in Sumatra, Cuban, and Connecticut Havana. 



Again, in follomng out an investigation on the relation of the nutrition 

 conditions to the quantity of oil formed in the seeds of such plants as 

 cotton, peanuts, and soybeans, the present writers (9) had occasion to 

 investigate the significance of the observation made by Mooers (19), that 

 successive plantings of certain varieties of soybeans {Soja max (L.) Piper) 

 made through the summer months, show a decided tendency to blossom 

 at approximately the same date regardless of the date of planting. In 

 other words, the later the planting the shorter is the period of growth up 

 to the time of blossoming. In the course of the investigation on oil forma- 

 tion it became desirable to study the possible effects of temperature dif- 

 ferences on the process. Since it is much simpler and cheaper to maintain 

 temperature differences during the winter by the use of heat than during 

 the summer by means of refrigeration, it was planned to make some tests 

 with soybeans during the winter. It was soon found, however, that the 

 plants began to develop blossoms before they had made anything like a 

 normal growth, and the few blossoms produced were cleistogamous, so 

 that it became necessary to abandon the plan of conducting the tests in 

 question during the winter months. As is the case with the Mammoth 

 tobacco, the time of year in which the plants are grown exerts a very 

 profound influence on growth and reproduction in the soybean. 



In seeking a solution of the problem as to why the behavior of these 

 plants is radically different from the normal during the fall and winter 

 months one naturally thinks of light and temperature as possible factors. 

 It was observed, however, that both the Mammoth tobacco and the 



