280 VEGETABLE PHYSIOLOGY 
a solution of chlorophyll is seen to be robbed of rays in 
these regions, and hence to present the appearance of a 
band of the different colours crossed by several dark bands 
(fig. 180). The greater part of the energy so obtained in 
the cells which contain the chloroplasts is at once expended, 
partly in constructing carbohydrate food materials and 
partly in evaporating the water of transpiration. The latter 
process is much the more expensive; recent observations 
have made it probable that 98 per cent. of the radiant 
E> 
Fic. 130.—ABsoRPTION SPECTRA OF CHLOROPHYLL AND 
XANTHOPHYLL. (After Kraus.) 
energy actually absorbed during bright sunshine is at once 
devoted to this purpose. 
When we speak of radiant energy we must remember 
that the rays of the visible spectrum do not supply all the 
energy which the plant obtains. It has been suggested by 
several botanists with considerable plausibility that the 
ultra-violet or chemical rays can be absorbed and utilised 
by the protoplasm without the intervention of any pigment 
such as chlorophyll. There is some evidence pointing to 
this power in the cells of the higher plants. Certain 
bacteria also construct organic material from simple com- 
pounds of nitrogen and carbon dioxide, though it is not 
probable that they utilise radiant energy directly. 
