THE PLANT A LIVING MACHINE. 19 



nected with the mode in which the chlorophyll 

 is concerned in utilising the energy of the 

 solar radiations. The point is one of supreme 

 importance, because it goes on all fours with 

 modern questions as to the rays of light ab- 

 sorbed or dispersed in our atmosphere at different 

 seasons of the year, or in special climatic con- 

 ditions, to say nothing of its other scientific 

 aspects. Unfortunately, however, we have no 

 satisfactory explanation of the actual role played 

 by the chlorophyll substance itself, in spite of 

 much industrious work which has been done in 

 the subject in this country and elsewhere. As 

 regards the rays employed, it was first proved 

 that the most effective belong to the red end of 

 the visible spectrum, and that the effect as 

 measured by the amounts of oxygen given off, 

 and of starch formed in given periods of time, 

 is more or less proportionable to the intensity 

 of the solar light. Then it was established that 

 no monochromatic light is so powerful as the 

 white light from which it was obtained, though 

 the relative numbers expressing the activity in the 

 red and yellow regions may stand to those in the 

 blue as something like 12 : i. The latest results 

 place the maximum assimilation in the red-orange, 

 and this coincides with the maximum absorption 

 in the chlorophyll. If we may accept the current 

 views as to the distribution of energy in the 

 spectrum of solar light, which depends on the 

 complete absorption of all the rays by a black 

 body, where they are estimated as heat, we have 



