64 



Influence of Solar Radiation on Plants. 



beans with nearly similar results, but beyond the observation 

 that " in proportion as the plants grew in height, in different 

 kinds of light, the number and size of their leaves diminished," 

 his attention appears to have been directed only to the question 

 of color.* 



Besides the experiments already detailed in this Eeport, and 

 those on wheat and Malope trifida described in my former one, 

 I have a few other observations on the effect of various qualities 

 of light on the growth of plants from the seed, which it may be 

 worth while briefly to record. They were made on the Collinsia 

 bicolor of the florists, and Mignonette. 



Seeds of the Collinsia were sown in garden mould in glasses, 

 and placed under the colorless, blue, yellow, red, and darkened 

 shades, on a table before a window which had a northwest aspect. 

 The perforated boards were used for supporting the glass covers. 

 The experiment was commenced on the 6th of July in last year. 

 On the 9th it was found that germination had taken place under 

 each glass except the yellow, where no plant grew until the 14th. 

 Under the colorless glass, the plants grew and nourished till the 

 beginning of August, when they all faded and died. Under the 

 blue and red glasses they grew well for a while, but began to 

 droop by the 26th of July. Those under the darkened glass ex- 

 isted rather longer, but they were tall and scraggy, and the 

 leaves did not fairly open. Only three plants germinated under 

 the yellow shade ; they were all unhealthy and died before the 

 26th. On August 4th, seeds were sown afresh under each glass. 

 Much the same order of growth was observed. 



On October 12th, a hundred seeds of Mignonette were sown 

 in each of seven glasses filled with garden mould. They were 

 placed about a third of an inch below the surface. Six of the 

 glasses were covered respectively with the colorless, blue, red, 

 yellow, obscured colorless, and obscured yellow shades, and the 

 seventh was placed in a dark closet. It should be observed that 

 the closet was rather warmer than the room. The Mignonette 

 seeds began first to germinate in the dark, then under the blue ; 

 then, after the lapse of a few days, they appeared under the red, 

 and colorless, and the obscured colorless glasses. The yellow 

 ray long retarded, and very nearly prevented their germination. 

 Those in the dark were tall, thin, and yellow ; they all died 

 about November 1st ; the others soon followed, excepting one 

 plant under the colorless glass, which was found still alive with 

 four green leaves on December 10th. 



The investigations of many experimenters have shown that 

 oxygen is necessary in the germination of seeds. The explana- 

 tion given is that that element is required for instituting the 

 action that converts the fecula of the cotyledon into sugar. It 



* From Ellis's " Farther Inquiries," &c. 



