Influence of Solar Radiation on Plants. 



61 



same manner for forty-eight hours. Their weight was then re- 

 duced to 66 grains, while those grown under the obscured color- 

 less (succulent as they were) lost in the same time only 14 grains; 

 and those under the obscured yellow appeared rather to have 

 gained weight. 



The increase in weight in these instances must be attributed, as 

 in the case of the wheat, to the absorption of water, and it seems 

 to be in almost reverse ratio to the healthiness of the plant ; for 

 those under the red, which had the best appearance at first, 

 showed by far the smallest increase in weight ; and those under 

 the blue, which were afterwards better looking, had not increased 

 greatly. 



In the comparative experiment made without any glass shade, 

 one pea began to germinate on May 23d ; this was shortly fol- 

 lowed by two others, but only one of the three grew to any size. 

 When measured on June 6th, its root was found to be only 0*75 

 inch long ; its stalk had attained a length of 4'5 inches ; its 

 leaflets were deep green, appearing as healthy as, if not healthier 

 than, any under the glass shades, and when removed from all 

 moisture for eighteen hours, it weighed 5*5 grains, showing an 

 increase of 2*7 grains on its original weight. 



On examining these results we are led to draw the following 

 conclusions, as far as peas are concerned, growing under the 

 conditions of the experiment. The cutting off of the chemical 

 rays favors the first germination of the seed, and this appears to 

 be the principal, if not the only advantage of the darkness ob- 

 tained by burying the seeds in the soil. The development of 

 roots also requires the absence of the chemical ray, yet it does 

 not go on to the greatest extent when all the solar influences are 

 excluded, but is favored rather than otherwise by heat and lumin- 

 osity. The first development of the plume also proceeds best 

 under the same circumstances ; yet these are not the conditions 

 which produce a healthy plant : if all the solar radiations be 

 withdrawn, whether entirely or only to a great extent, the plants 

 absorb much water and grow very tall, without developing 

 secondary branches or many leaves. The whole force of these 

 radiations, on the contrary, prevents or greatly impedes the 

 growth of these plants under the circumstances of the experi- 

 ment. As peas grow commonly in the full sunshine, it would 

 be interesting to observe whether the negative result obtained 

 arose from the absence of soil about the roots, from excessive 

 moisture, or from some other cause. The experiment, however, 

 affords us no data for determining this question. The chemical 

 force is the most antagonistic to the growth of the pea, and 

 luminosity also militates against it : the heating rays are favora- 

 ble ; but let the plant be fairly established, and those radiations 

 which are comparatively speaking devoid of light, but replete 



