10 



EFFECTS OF AKTIFICIAL SHADING ON PLANT GROWTH. 



the measurements found to be in practical agreement with those made 

 by means of the "printing-out" photographic paper. 



The cloths designated in Table II were used and gave reductions in 

 light intensity as indicated after each. The expressions n, n/2, n/93, 

 etc., are convenient in referring to normal illumination, one-half 

 normal illumination, one ninety-third normal illumination, etc. 



Table II. — Sectional coverings and light intensities. 



Section. 



Cloth. 



Fraction of normal 

 light. 



1 



2 



3 



4 



5 



6 





1/93 or n/93. 

 1/15 or n/15. 

 l/7orn/7. 

 1/5 or n/5. 

 1/2 or n/2. 

 1 or n. 



Light canvas cloth (black) . . 

 Chambray 





Voile 







Natural-size prints, made by placing the cloths used on the 

 "printing-out" paper and exposing them to full sunlight, are repro- 

 duced in Plate I, figure 2. These prints show the texture of the 

 different cloths and indicate their comparative efficiency in reducing 

 light intensity. 



TEMPERATURE. 



Air temperatures under each section were read every day at 6 a. m., 

 at noon, and at 6 p. m.; and a thermograph record was taken in 

 section 1 of each bed. The temperatures of the soil at the surface 

 and at a depth of 8 inches were read at the same time. It must be 

 understood that the differences which would naturally result from 



25* C 



20°C 



I5°C 



&£Z> 



BETD B 



_^C»L._ 



50.^ 



Fig. 2.— Diagrams showing temperatures at 6 a. m., averaged for the entire period of the experiments, 



shading would not show markedly except at or near the period of 

 maximum light. It is therefore evident that the morning and evening 

 determinations should show only slight differences under the different 

 shades. 



The mean temperatures as recorded at 6 a. m. are shown in figure 2. 

 There was no appreciable difference in the temperatures recorded in the 

 two beds b nor for that matter under the different shades. The air 

 temperatures averaged about 4° C. below the soil temperatures at the 

 depth of 8 inches, and approximately 2° C. below the temperature of 

 the soil surface. These results are due to the retention of a portion 

 of the heat absorbed by the soil on the previous day. 



279 



