110 EXPERIMENT STATION RECORD. 



under the red light. Those in the green hothouse yielded about one- 

 tenth as much as those in the white. The weight of the fruits from the 

 blue hothouse was insignificant. The strawberries which received only 

 colored light were very watery and insipid. Their average weight was 

 half that of those which had received the total radiation. 



The different rays of the solar spectrum modify not only the above- 

 ground growth of plants, but also affect the entire vegetative part of 

 the plant. The root system of the young plants which had been grown 

 in hothouses was poorly developed. It was greatly reduced in the red 

 house, and in the blue there was almost no root system. The weight 

 of the roots of the sensitive plants in the different houses, October 13, 

 was as follows: In the white house, 5 gin.; in the red, 1.0 gm.; in the 

 green, 0.09 gm.; in the blue, 0.05 gm. 



The nutrition of the plant is to a great extent dependent upon the 

 root system. It is partly due to this dependence that the plants in the 

 red, blue, and green houses had so little vigor. It is well known that 

 the red and orange portions of the spectrum favor assimilation, trans- 

 piration, and respiration ot plants. The natural result of this is an 

 increase in the vegetative activity and in the function of nutrition. It 

 is evident, therefore, that differences of growth, vegetative activity, 

 vigor, development, sensitiveness, and coloration of plants result from 

 differences in radiation. Microscopic examination of sections of the 

 sensitive plant showed that the anatomical structure and the diameter 

 of the plants in the red and white houses differed. The epidermis was 

 thicker, and the woody fibers of the stem were more numerous in the 

 plant in the white hothouse, the pith was much less developed, the cells 

 were better formed, and the partitions thicker. 



Notwithstanding the great care which was taken in conducting these 

 experiments, it was very difficult to avoid all sources of error. Glass 

 considered monochromatic for the red as well as for blue proved unsat- 

 isfactory for the reason that some yellow rays passed through them. 

 In further study of this subject, experiments were conducted in which 

 the three different colors were obtained from the spectrum derived from 

 a prism. 



Plants were placed in the different regions of the solar or electric 

 spectrum and the modifications due to different rays thus observed. 

 For this purpose a prism was constructed capable of giving a spectrum 

 of great dimensions, and in which could be placed such liquids as car- 

 bon bisulphid aud spirits of turpentine, the refractive power of which 

 is very high. The source of light was an electric arc lamp. The use 

 of carbon bisulphid was discouiinued on account of its volatility and 

 excessive inflammability, and as a substitute spirits of turpentine, the 

 refracting power of which is far less, was used. The index of refrac 

 tion for spirits of turpentine is 1.470496 for the red and 1.493874 for the 

 violet. The difference in dispersion of the two is, therefore, 0.023378. 

 A straight slit was placed against the prism filled with turpentine and 



