Mar. 1, 1920 Effect of Length of Day on Plant Growth 567 



VIOLETS (viola fimbriatula sm.) 



A common wild species ranging from Nova Scotia to Wisconsin and 

 southward and growing in sandy fields and on dry hillsides. The normal 

 blooming period comes in April. Exposed to light from 9 a. m. to 4 p. m. 

 Two lots of six plants were transferred from the field to two boxes meas- 

 uring 3 feet by 10 inches by 10 inches on June 9, and one of the boxes was 

 placed at once in the dark house. The test plants showed flower buds as 

 early as June 21 and were in blossom early in July, producing purple, 

 petaliferous flowers and also cleistogamous flowers. The control plants 

 produced numerous cleistogamous flowers but none of the purple, petal- 

 iferous type. 



EARLY GOLDENROD (SOLIDAGO JUNCEA AIT.) 



The earliest species of goldenrod, ranging from New Brunswick to 

 Saskatchewan and south to North Carolina and Missouri. Blossoming 

 normally extends from late June to September. Exposed to light from 

 9 a. m. to 4 p. m. Two lots of six plants were transplanted to two boxes 

 measuring 3 feet by 10 inches by 10 inches on June 6, and one of the 

 boxes was at once placed in the dark house. The test plants and the 

 controls blossomed at the same time, late in August. The test plants 

 however, were shorter and more compact than the controls. The heights 

 of the test plants averaged 24 inches and those of the controls 38 inches. 

 The test plants advanced toward maturation more rapidly than the con- 

 trols after the flowering stage had been reached. 



EFFECT OF RESTORING THE TEST PLANTS TO NORMAL LIGHT 

 EXPOSURE AFTER BLOSSOMING HAD OCCURRED 



In the experiments with soybeans, aster, and ragweed described above 

 it has been made clear that after blossoming has occurred the effect of 

 shortening the daily exposure to sunlight is to hasten greatly the ripen- 

 ing of the seed. In certain instances, however, as has been recorded 

 under the several experiments, the test plants were restored to the 

 normal light exposure as soon as blossoming had occurred. 



Under these conditions seed pods of the soybeans ripened rapidly, th^ 

 leaves turned yellow, and for a time it appeared that the plants would 

 die as is normal for the soybean. Eventually, however, new branches 

 developed under the influence of the long summer days. The renewed 

 growth was especially well-developedin the Biloxi variety, and the final 

 result was that these plants, still bearing the first crop of ripened seed 

 pods, blossomed for the second time September 4 to 8. This date of 

 blossoming, moreover, is also that for the first blossoming of the control 

 plants which had been planted on the same date as the test plants and 

 had been exposed to the nonnal daylight period throughout their de- 

 velopment. 



Like the soybeans, the asters after a time responded to the long-day 

 influence; and by July 20 the plants, though bearing ripened seed, were 



