Mar. 1, 1920 Effect of Length of Day on Plant Growth 599 



Seed of radish (Raphanus sativus L.)> Scarlet Globe/ was sowep 

 November i, 1919, coming up in both lighted and unlighted houses 

 November 5. On February 12 the control plants, although more stocky 

 and having larger roots, showed no indications of developing flower 

 stems. In the lighted house, however, the plants had developed smaller 

 roots, and flower buds were plainly in evidence, showing that the plants 

 would soon blossom, as is their normal behavior in response to the 

 long summer days out of doors. 



Seedlings of the Maryland Mammoth variety of tobacco were trans- 

 planted to 1 2 -quart iron pails on November 10, on which date they were 

 placed in the control and the lighted houses. The control plants, six in 

 number, exhibited the typical behavior of winter-grown Maryland 

 Mammoth plants, all blossoming during the period from December 31 

 to January 8. The plants in the lighted house, six in number, behaved 

 as typical summer-grown mammoths, becoming very compact, stout and 

 leafy, with no indications of blossoming on February 12. On this date 

 these plants had already produced many more leaves than the control plants. 



Bulbs of Freesia refracta Klatt were placed in soil in 5-inch pots on 

 July II, 1919. Four pots of these plants were kept in the large dark 

 house previously described from 4 p. m. to 9 a. m. daily from July 23 

 till November 15, when they were transferred to the greenhouses, two 

 pots being placed in the control house and two in the lighted house. 

 None of these pfants when taken from the dark house on November 15 

 showed any indications of blossoming. Both lots began blossoming 

 about December 27. In the control house, however, the plants produced 

 many flower stalks and continued to blossom profusely for a long period. 

 The plants in the lighted house, on the contrary, produced but few 

 flower stalks and few blossoms and soon ceased blooming entirely. 



Large, robust clumps of wild violets, of the species Viola papilionacea 

 Pursh, were transplanted to pots and boxes and placed in the control and 

 lighted houses on October 31, 191 9. At the time these plants were 

 removed from the field the abnormally warm autumn weather had 

 forced them into bloom, and many purple, petaliferous blossoms were in 

 evidence. As the winter days continued to shorten naturally in the 

 control house, blossoming was suppressed and no new leaves were pro- 

 duced. These control plants appeared to be almost dormant, except 

 for the production of numerous short, thickened stems which were 

 crowded close to the ground among the old leaves. In the lighted house 

 the production of the purple, petaliferous blossoms also ceased, but vege- 

 tative growth was initiated and new leaves appeared in great abundance. 

 Coincident with this marked vegetative activity, the plants continuously 

 produced fertile, cleistogamous flowers in great abundance. This fur- 

 nishes another example of ever-blooming in response to a favorable length 

 of day. In all respects this behavior of the violets in the lighted house 



' Horticultural variety. 



