Influence of Solar Radiation on Plants. 59 



peas soaked in water were placed on the bricks along with the 

 wheat seeds, on April 21st. On the 24th they were found to be 

 swollen and beginning to burst. The seeds under the yellow, 

 obscured yellow, and obscured colorless glasses, were the more 

 rapid in their first development. On the 29th, the plumes began 

 to appear under the obscured colorless, yellow, and red shades, 

 and two days afterwards under the blue and colorless. The 

 plants under the obscured yellow glass appeared very unhealthy. 

 The radicles grew astonishingly under the yellow glass, and be- 

 came very long under the red and obscured colorless. On May 

 8th, the plants in complete or partial obscurity were found to be 

 several inches high; under the red, 2 inches; under the yellow, 

 not quite so much ; while even on the 11th, the plants under the 

 blue had only j ust developed themselves, and under the colorless 

 glass only one seed had put forth a stalk, and that was but half 

 an inch in length. 



On the 12th they were more fully examined, and drawings 

 were made. Under the colorless glass, the peas resembled the 

 plume only in the first stage of development, the principal root 

 short and thick, with short and thick secondary rootlets, all 

 fringed with hairs. Under the blue, the peas were in a somewhat 

 more advanced stage. Under the red, ten plants had grown, — 

 roots straggling, stalk bending towards the light, with many 

 leaflets of a deep green color. The plants under the yellow 

 glass were characterized by enormous roots, which turned away 

 from the light in a very marked way. Nine of those under the 

 obscured colorless had long roots, long succulent weak stalks, 

 and pale green leaflets. Under the obscured yellow, the plants 

 appeared for the most part with smaller roots, though two of 

 them, which were nearest the light, had grown with a stalk. In 

 the dark, six of the peas had grown, — roots irregular, having 

 few side-rootlets, stalks succulent, but tolerably erect, bearing 

 yellow leaflets. The plants in the red light continued to grow 

 healthily, some being 6 inches high on the 15th; under the 

 yellow and obscured yellow, they also grew healthily ; under the 

 obscured colorless, the stalks were found on the 22nd no longer 

 capable of supporting themselves. The stalks in the dark were 

 at the same time erect, and 10 inches in length. On the 26th, 

 the seeds under the colorless glass were found to have made 

 scarcely any advance since the 12th. Under the blue, one had 

 grown tall and healthy, but the rest were very small. Under 

 the red, the plants were growing healthily as on the 12th, but 

 some of them had attained the height of 9 inches, and bore three 

 or four secondary branches. Those under the yellow had grown, 

 but did not appear healthy. Under the obscured colorless glass, 

 the plants had grown since the 12th about as much as might 

 have been expected from the time, but they were very weak. 



