54 



Influence of Solar Radiation on Plants. 



yellow glasses ; but the flower under the red glass showed no 

 trace of red color, even when it had quite shrivelled up, nor was 

 there any such change in the intense purple that appeared where 

 light was excluded. 



In such experiments as those just detailed, it is difficult to 

 separate what might be the effect of adventitious circumstances 

 from the genuine effect of the diversity of light. However, we 

 may safely remark in the experiment which was conducted in 

 perfect obscurity — the rapid and abundant growth of thin root- 

 lets, the general healthiness of the plant, the non-formation of 

 chlorophyll, but the production of the coloring matter of the 

 flower, not altered in its subsequent fading. The two experi- 

 ments performed in partial obscurity appeared as closely alike 

 as possible, until the last week, when one of the plants died. 

 The fact that the chemical rays were cut off from one of them, 

 made no apparent difference. Their backwardness as compared 

 with the other flowers, was probably owing to their having been 

 placed in a position which was somewhat colder than that of those 

 which received the full light of the sun. The effects of obscu- 

 rity were observable in them in a modified manner, and they 

 both absorbed much more water than the other plants did. The 

 effect of the red glass in interfering with the length of the roots, 

 and in producing a badly developed plant, was observed both in 

 this and in the former series of experiments. Its power of pre- 

 venting the reddening of the faded flower is remarkable. The 

 effect of the yellow glass in causing the rootlets to be few and 

 straggling, and in diminishing the absorption of water, was also 

 noticed in both instances. The blue glass appeared to favor the 

 development of the hyacinth. 



That the green coloring matter of leaves requires the action of 

 light for its production, has long been universally admitted, and 

 Dr. Daubeny has shown that it depends on the luminous ray. 

 From analogy, and from a few observations by Davy, Senebier, 

 and others, the same has been assumed to hold good in respect 

 to the colors of flowers, but the purple hyacinth bears other 

 witness, and should induce us to doubt this too hasty con- 

 clusion. 



A number of experiments on germination were made during 

 the spring. The seeds experimented on were those of the wheat 

 and the pea ; and in every case both were employed, in order 

 that if there should be a different effect of light on the monoco- 

 tyledonous and dicotyledonous plants, it might be seen. Seeds 

 of familiar plants and of great commercial importance were 

 chosen, as it was supposed a greater degree of interest would 

 naturally attach to experiments on them, and it might happen 

 that some observations of value to the agriculturist might be 

 made. 



