66 



Influence of Solar* Radiation on Plants. 



The effect of oxygen on the germination of wheat and peas 

 under the influence of the different solar radiations was also 

 tried. The small colored glasses, having a capacity of 172 to 

 177 cubic inches, were employed, and the experiments were con- 

 ducted like those under the colored shades which have been 

 already detailed. The seeds were placed on the bricks on May 

 2nd. On the 8th, both the wheat and the peas had burst under 

 the colorless glass, but they soon became mouldy, and before the 

 end of the month they were quite dead. The seeds under the 

 yellow glass ran much the same course ; but those under the blue 

 glass, though they did not burst till the 11th, grew well, and by 

 the 26th two of the wheat plants had attained a height of 4 or 5 

 inches. The experiment was discontinued on June 5th. The 

 plants were removed from the brick for desiccation, and on the 

 following day the five of the wheat which had germinated were 

 found to weigh 8 grains, giving an average of 1*6 grain for each, 

 or an increase of 0'9 grain on the original weight. All the six 

 peas had germinated and weighed 26 grains, giving an average 

 of 4*3 grs. for each, or an increase of 1*6 grain on the original 

 weight. 



Thus far I have proceeded in the investigation. Many inter- 

 esting inquiries naturally suggest themselves ; some have been 

 already alluded to, for instance, the influence of light upon the 

 colors of flowers ; the amount of exclusion of light effected by 

 the soil; the different condition of solar influences required" by 

 wheat or by peas at later periods of their growth ; and the ex- 

 tension of the observations to other seeds. Other questions might 

 be raised, such as,— What character of light promotes best the 

 absorption of oxygen in germination ? At what period in the 

 growth of a plant does oxygen become unnecessary ? Is oxygen 

 requisite for the full development of a bulbous-rooted plant ? 

 Does carbonic acid act specifically in the prevention of germina- 

 tion, or merely by the exclusion of oxygen ? How far does the 

 rapid development of a plant in an early stage interfere with its 

 healthy growth at a later period ? 



