AND OF LIGHT. 24? 



gradually increases, and reaches a maximum at day- 

 break. It then diminishes to a minimum a little before 

 sunset, after which it rises again. 



It is not to be imagined that because daylight retards 

 growth it is unfavourable to the proper develop- 

 ment of a plant. For instance, Karsten * found 

 that whilst a kidney bean reared in the dark for a 

 month or two weighed 20 per cent, more than one 

 reared in the light, yet the leaves did not weigh a 

 fifth as much. Again, Clayton t allowed six bean 

 plants to grow in a spot where they would catch 

 all the sunshine of the day, whilst six other similar 

 plants were protected by a boarding, which effectu- 

 ally screened off the sun. When freshly gathered 

 in October, the weight of the beans and pods of the 

 exposed plants was to that of the protected as 99 : 29, 

 whilst the weight of the dry beans was as 16 : 5. The 

 next year, the weight of the fresh beans and pods ob- 

 tained from the sunshine-grown seed of the previous 

 year was half as much again as in the case of the plants 

 from shade-grown seeds, in spite of the fact that all of 

 the plants were now grown in sunshine and under pre- 

 cisely similar conditions. " In the fourth year plants 

 with an exclusively shady ancestry produced flowers, 

 but failed to mature fruit." 



The intensity of the light to which a plant is exposed 

 may considerably affect its form and structure, as well 

 as its rate of growth. Thus the effect of direct sun- 

 light, as compared with diffused light, on the absolute 



*Landw. Versuchs-Stat. , xiii. p. 176. Quoted from Davenport's 

 " Experimental Morphology," p. 419. 

 f Nat. Science, xi. p. 12. 



