EFFECT OF LIGHT ON PLANTS GARNER AND ALLARD. 571 



There are numerous varieties of soy bean, some of which can be 

 successfully grown only in southern latitudes, because in more north- 

 erly regions they are killed by frost before the seed can be matured. 

 Thus the variety known as Biloxi when planted as early as April in 

 the latitude of Washington, D. C, does not begin to flower till Sep- 

 tember, although certain other varieties under the same conditions 

 will show open blossoms early in June. Experimental plantings of 

 the Biloxi made at Washington in April have required 125 days to 

 reach the flowering stage, while similar plantings of the Mandarin 

 variety required less than 40 days. A peculiarity of the Biloxi is 

 that as successive plantings are made through the spring and sum- 

 mer the number of days required to attain the flowering stage 

 is markedly reduced, and plantings made as late as August 5 have 

 required only 55 days to flower, while the Mandarin shows no such 

 shortening of the vegetation or growing period. The Biloxi shows 

 this peculiarity each year in spite of decided differences in tempera- 

 ture and rainfall which occur in the different years. Why this 

 marked shortening in the growing period of the Biloxi as the season 

 advances? The potential advantage of the response to the advancing 

 season is readily seen, for curtailment of the growing period mate- 

 rially favors the ripening of seed before cold weather, and therefore 

 tends to increase the northward range of the plant. A distinction 

 must be made here, however, between advantage and cause. To 

 assign the danger of destruction by cold as a cause of the speeding 

 up of flower and seed formation would be to assume that the plant 

 is able to anticipate the advent of cold weather and to modify its 

 course of development accordingly. Before considering further this 

 response of the Biloxi soy bean to the advance of the summer season 

 it will be of interest to review briefly the somewhat similar behavior 

 of a variety of tobacco {Nicotiana tabaeum L.) known as Maryland 

 Mammoth. 



The Maryland Mammoth tobacco differs from its parent type, 

 Maryland Narrowleaf. in that when grown in Maryland during the 

 summer months the plant continues to increase in height without 

 flowering till October or November or until killed by cold weather. 

 The parent type produces about 25 leaves per plant while the Mam- 

 moth may produce more than 100 leaves. If the plant is transferred 

 to the greenhouse in the fall, growth will continue till November, 

 when flowering occurs. If seedlings are propagated during the 

 winter months they invariably flower without growing larger than 

 the ordinary varieties of tobacco. Finally, while the primary and 

 axillary shoots developing during the winter and early spring in- 

 variably flower without delay, there comes a time in the spring when 

 the new shoots of the plant assume the summer type of growth — 

 that is, they continue to grow indefinitely without flowering. Thus, 



