GENERAL DISCUSSION. 27 



themselves in the deepest shade in the early part of the experiments, 

 they made practically no growth in a light intensity of n/15 or less. 



The effect of the reduction of light upon the flavor of lettuce was 

 very marked. With a reduction to n/5 the flavor of lettuce was 

 noticeably improved and the growth was still somewhat better than 

 in full light. The flavor of radish was not perceptibly changed by 

 shading. 



The effect of the equalization of temperature, due to the introduc- 

 tion of the fan in one of the beds, was in most cases very slight. In 

 the case of the potato the growth in the bed with the fan seemed to 

 be considerably better than in the other. In all probability this was 

 not due to the action of the fan itself, for the reason that in sections 4 

 and 5, far removed from the fan, the differences were greater than in 

 sections 2 and 3, which were nearer to the fan. In fact, careful ob- 

 servations of the beds at the end of the experiment led to the con- 

 clusion that the effects resulting from changes in temperature, 

 humidity, and even wind movement, were negligible as compared 

 with those resulting from differences in illumination. As far as the 

 evidence from these experiments go, the effects noted in shade ex- 

 periments are attributable to reduction of the light intensity and not 

 to any appreciable extent to the resulting differences in other factors. 



In general, we may say that the growth of the plants with which 

 experiments were made was not as good, measured by the general 

 appearance of the plants, height, green weight, and number of nodes, 

 in full light as it was in the light from n/2 to n/5. Some of these 

 plants were able to grow in a light reduced to n/7 almost as well as 

 in full sunlight. A reduction of the light to n/15 cut down the growth 

 very perceptibly, although all of the plants, with the exception of 

 corn in bed B, were able to keep alive even under this condition. 

 When the light was reduced to n/93 the only plants which survived 

 were cotton and potato. The potato plants were in a dying condition 

 at the end of the experiment, and the cotton had made no growth, 

 but was able to keep alive and in good condition even with this 

 degree of shading. The probable reason for the failure of these 

 plants to grow in light less than n/15 was their inability to manu- 

 facture carbohydrates. The plants were green colored and had 

 developed chlorophyll, but were unable to increase in size after the 

 reserve material of the seed or the tuber was exhausted. Corn 

 showed very little ability to continue growth even with n/15 light. 

 This amount of light reduction apparently marked almost the limit 

 for carbon assimilation in all of the plants used. 



The amount of solar energy utilized directly in the process of 

 photosnythesis has been accurately calculated by Brown and Es- 

 comb (1905), and is a surprisingly small proportion of the amount of 



279 



