52 



Influence of Solar Radiation on Plants. 



retard their growth, and that the luminous and calorific ra}^s had 

 peculiar actions of their own, 



As to the leaves, little appearance of growth was observable 

 in any of the hyacinths till December 26th, when those under 

 the colorless and blue glasses began to shoot; that under the red 

 glass followed very soon, while those under the yellow and the 

 partially and wholly obscured glasses gave no sign for about 

 three weeks longer. The leaves grew most rapidly in the blue 

 light. The following comparisons of the length of the leaves 

 under the various luminous influences may be interesting. They 

 were taken on the 13th and 21st of February, when all the 

 plants were in vigorous growth, but not one of them had 

 flowered, and on March 22nd, when the plants had attained their 

 full maturity. 





February 13. 



February 21. 



March 22. 



" blue « 



" red " 



" obscured colorless glass, . . 

 " obscured yellow " 



4 inches 

 6 " 

 3 " 



2 " 



3 " 

 3 " 

 3 « 



6 inches 

 8 " 

 5 " 



3 " 



H " 



3£ " 



4 " 



11 inches 

 14 " 



11 " 

 8 " 



10 " 



12 " 

 10 " 



The flower-stalk very nearly kept pace with the leaves. There 

 was a greater difference in the periods at which the petals 

 opened than in the former series of experiments; those under 

 the blue and colorless glasses took the lead, and those under the 

 partially obscured glasses were the last. They opened for the 

 most part during the last days of February. Under the red 

 shade two flowers grew, but they were thin and straggling : the 

 same w r as the character of the plant that grew in the dark. 

 There were two flower-stalks under the partially obscured color- 

 less glass; they were never developed, however, but were found 

 at the end of March losing their color and becoming rotten. 

 The experiments were terminated on March 22d, excepting the 

 two under the partially obscured glasses, which were allowed to 

 continue till the 30th. The respective lengths of the flower- 

 stalks were then, — • 



Under the colorless glass 13 inches. 



blue " 13 



" red " 12-5 " 



yellow " 12 



" obscured colorless glass 4 



" obscured yellow " 10 



dark " 13 " 



The hyacinths having been removed from the water in which 

 their roots had been immersed, were suffered to dry in the open 

 air of the room for twenty -four hours, and were then weighed. 



