248 SPH^RELLA CHAP. 



is reason for thinking that it is the protoplasm of these 

 bodies and not the actual green pigment which is the 

 active agent in the process. 



Moreover, it must not be forgotten that the decom- 

 position of carbon dioxide is carried on only during 

 daylight, so that organisms in which holophytic 

 nutrition obtains are dependent upon the sun for 

 their very existence. While Amoeba derives its energy 

 from the breaking down of the proteids in its food 

 (see p. 235), the food of Sphaerella is too simple to 

 serve as a source of energy, and it is only by the help 

 of sunlight that the work of constructive metabolism can 

 be carried on (photosynthesis) . This may be expressed by 

 saying that Sphserella, in common with other organisms 

 containing chlorophyll, is supplied with kinetic energy (in 

 the form of light or radiant energy) directly by the sun. 



As in Amoeba, destructive metabolism is constantly 

 going on side by side with constructive. The proto- 

 plasm becomes oxidised, water, carbon dioxide, and 

 nitrogenous waste matters being formed and finally got 

 rid of. Obviously, then, absorption of oxygen must 

 take place, or, in other words, respiration must be one 

 of the functions of the protoplasm of Sphaerella as of 

 that of Amoeba. In many green, i.e., chlorophyll- 

 containing, plants, this has been proved to be the case : 

 respiration, i.e., the taking in of oxygen and giving out 

 of carbon dioxide, is constantly going on, but during 

 daylight is obscured by the converse process the 

 taking in of carbon dioxide for nutritive purposes and 

 the giving out of the oxygen liberated by its decomposi- 

 tion. In darkness, when this latter process is in abeyance, 

 the occurrence of respiration is more readily ascertained. 



Owing to the constant decomposition, during sunlight, 

 of carbon dioxide, a larger volume of oxygen than of 

 carbon dioxide is evolved ; curd if an analysis were made 



