24 



EFFECTS OF ARTIFICIAL SHADING ON PLANT GEOWTH. 



Table X. — Diameter of stem at end of 50 days, in percentages of diameter of stem in 



normal light. 



Bed and plants. 



Section number and light intensity. 



1, n/93. 



2, n/15. 



3, n/7. 



4, a/5. 



5, n/2. 



6, n. 



Bed A (with fan): 



53 

 

 



80 

 71 

 



67 

 86 

 32 



67 

 71 

 32 



93 

 143 



84 



89 

 86 

 84 



80 

 171 

 105 



93 



86 

 84 



107 

 143 

 95 



80 

 143 

 105 



100 





100 





100 



Bed B (without fan): 



100 





100 





100 







In number of nodes (Table XI) the plants grown in n/2 to n/7 

 light usually exceed those grown in normal light except for cotton 

 in n/7 light. With a light reduction of n/15 or more the number of 

 nodes produced was greatly reduced except in the case of potatoes. 



Table XI. — Average number of nodes per stem at the end of 50 days, in percentages of 

 number developed in normal light. 



Bed and plants. 



Section number and light intensity. 



1, n/93. 



2, n/15. 



3, n/7. 



4, n/5. 



5, n/2. 



6, n. 



Bed A (with fan): 



Potato 



84 

 

 



97 

 18 

 



103 

 55 

 67 



91 



18 

 40 



168 

 91 

 107 



116 



91 



107 



161 

 127 

 133 



148 

 109 

 133 



136 

 146 

 120 



123 

 127 

 107 



100 





100 



Radish 



Bed B (without fan): 



100 

 100 





100 





100 







EFFECT OF SHADE ON THE THICKNESS OF LEAVES. 



Leaf prints made by exposing a series of selected leaves for a suffi- 

 cient length of time to produce a print on a photographic "printing-- 

 out" paper, give a very good idea of the relative absorption of light 

 by the different leaves. Leaves which have developed in full light are 

 thicker and give lighter colored or whiter prints than the thinner 

 leaves which have been grown under shades. 



In corn (PL III, fig. 2), though a slight difference can be noted 

 as between normal (No. 6) and n/2 (No. 5) light, and a more marked 

 difference as between n/2 and n/5 (No. 4), practically no difference 

 can be noted in the shades of the prints from leaves produced under 

 a light intensity of less than n/5. Only a comparatively slight differ- 

 ence is shown in this series of prints, which indicates that in corn 

 there was only a slight modification in thickness of the leaf and density 

 of the chlorophyll as a result of this variation in the physical environ- 

 ment. 



279 



