EFFECT OF DIFFERENT LIGHT INTENSITIES ON PLANTS. 



17 



It should be noted that the plants in bed A (that in which the fan 

 was operated) were much taller and heavier than those in bed B. 

 (Tables IV, V, VIII, and IX.) Since the difference showed most 

 markedly in shade 5, winch was so far removed from the fan as to 

 make it practically impossible to detect the air current, the writer 

 is inclined to regard it as produced by some factor other than those 

 especially considered in this paper. 



The potato could elaborate no food material and in fact developed 

 no leaves in the deepest shade. In n/15 light the leaves were very 

 small, and no food material, or at least very little, was elaborated, 

 since when once the plants had exhausted the reserve food supply 

 there was no further increase in weight, the weights at the end of 50 

 days having been less than at the end of 30 clays. With a light 

 intensity varying from n/7 to n/2 growth was greater than in full light. 



Fig. 8.— Relative sizes of potato plants 30 days after the beginning of growth. The numbers correspond to 

 those of the shades and the letters indicate the two beds in the experiment. (Traced from photograph.) 



The relative size of the plants after 30 days (fig. 8) and 50 days 

 (fig. 9) shows the increased growths in light n/2 to n/7; also the 

 limited growth in n/15 and n/93 light. As long as the food supply 

 of the tuber was adequate to the needs of the plants they grew as well 

 under the deeper shades as in the more intense light; but as soon as 

 the food supply failed, it became evident that a fight intensity of n/15 

 or less was insufficient for food manufacture. Small leaves, which were 

 normally green developed in n/15 light, but apparently little or no 

 starch formation could take place. 



COTTON. 



In some ways the results of shading cotton were more interesting 

 than those obtained with any other plant. The weight of the cotton 

 plants showed a considerable increase at the end of 30 days even in 

 n/15 and n/93 light. In n/7 to normal light no great differences 



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