24$ SPH^ERELLA CHAP. 



is a function of chlorophyll, or to speak more accurately, of 

 chromatophores, since there 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 decomposition 

 of carbon dioxide is carried on only during daylight, so that 

 organisms in which holophytic nutrition obtains are depend- 

 ent 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 Sphserella 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. This may be expressed by saying that 

 Sphaerella, 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 protoplasm 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 pro- 

 toplasm 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 decomposition. In 

 darkness, when this latter process is in abeyance, the occuf- 

 rence <>l ivspinm'on is more readily ascertained. 



Owing to the constant decomposition, during sunlight, of 

 carbon dioxide, a larger volume of oxygen than of carbon 



