578 Journal of Agricultural Research voi. xviii. no. u 



blossoming did not occur till October ii, 109 days after germination. 

 The fact that this plant does not blossom here till the middle of October 

 indicates that the critical length of day for flowering can not be much 

 in excess of 12 hours; and the physiological minimum for the vegetative 

 period appears to be approximately 28 days, about the same as for the 

 Biloxi soybean. This bean would seem to be admirably adapted to 

 tropical conditions. 



The writers are informed by Dr. Shoemaker that in tests made by him 

 at Washington this species in the greenhouse blossomed freely during the 

 winter and developed seed. In the spring some, of the plants, having 

 been transferred to pots after the tops had been largely removed, were 

 placed out of doors. New shoots developed, and these grew throughout 

 the summer without blossoming. It is clear that this plant behaves like 

 the Mammoth or giant type of tobacco toward differences in the length 

 of day. 



Ragweed is still another example of a short-day plant, for, under a 

 7-hour exposure, the anthers of the staminate heads were shedding 

 pollen freely within 27 days after the beginning of the test, while under 

 outdoor conditions blossoming did not occur till 7 weeks later. Radish 

 is a good example of the type requiring a long day for attainment of the 

 flowering stage, for, like Mikania, it has not been able to blossom under a 

 7-hour exposure although the test was continued throughout the sum- 

 mer, while under outdoor conditions blossoms appeared one month after 

 germination. Throughout the test the rosette type of leaf development 

 was maintained under the shortened light exposure, and both leaf and 

 root continued to grow; so here, once more, is apparently a manifesta- 

 tion of gigantism. Under the conditions of the tests, the two biennials, 

 cabbage and carrot, showed no decided response to shortened light 

 exposure so far as concerns flowering; but their behavior under normal 

 conditions indicates that they are to be regarded as typically long-day 

 plants. Hibiscus is a striking example of a long-day plant, for not only 

 is it unable to blossom under a 7-hour light exposure but it is also unable 

 to make any appreciable growth under these conditions. The behavior of 

 Viola is of interest because of the habit of forming both cleistogamous and 

 chasmogamous flowers, the two types appearing at dififerent seasons. It 

 appears that the later developing cleistogamous flowers are to be regarded 

 as forming the more distinctively reproductive organs. Under a 7-hour 

 light exposure, which was not begun till June 7, the plants showed open, 

 purple, petalliferous flowers during the first week in July, although, of 

 course, a previous crop of these blossoms had been produced earlier in the 

 season. The cleistogamous blossoms appeared also on the plants at the 

 usual time, in June. The early goldenrod used in the tests showed no 

 shortening of the vegetative period under a 7-hour exposure. 



