Mar. I, 1920 



Effect of Length of Day on Plant Growth 585 



a. m. to 8 a. m. and from 2 p. m. to 4 p. m. and increases very rapidly 

 from 8 a. m. to 6 a. m. and from 4 p. m. to 6 p. m. For vertical exposures 

 the reverse relations, of course, obtain. 



Table V. — Computed shading effect of netting of various weaves and of cheesecloth at 

 different hours of the day during the summer months, with horizontal exposure of the 

 netting and cheesecloth and also with vertical exposure of the cheesecloth 



[Complete shading represented by unity] 



To obtain further information as to the shading eflfect of the nettings 

 used, a section of the simplified type of shade, without side covering, 

 was set up and covered with the 12 by 12 netting. Under this shade 

 (about 6 inches below the netting) Livingstone standardized black and 

 white spherical atmometer cups were installed, and corresponding control 

 cups were placed in full sunlight in the open air. In general, it was found 

 that satisfactory results could not be secured when the wind was blowing; 

 but when there was no appreciable breeze, readings were obtained which 

 seemed to indicate a coefficient of light transmission reasonably close to 

 that determined by Prof. Kimball. Typical readings obtained on clear, 

 calm days are given in Table VI. 



Table Yl.— Readings of black and white spherical atmometer cups under 12 by 12 netting 

 and in direct sunlight, and the indicated coefficient of light transmission, igig 



In the 1 91 6 experiments the soybeans were planted June 21, and the 



shade was placed in position July 5. Detailed observations were made 



on the growth and development of the shaded plants and of the unshaded 



controls. There were 93 individuals under the shade and 67 in the 



160115°— 20 3 



