ANAEROBES 257 



that certain plants may exist with only intramolecular respiration 

 during the seedling stage, and many Phanerogams are probably 

 anaerobic to a similar extent. An increasing capacity for non- 

 atmospheric respiration is to be found among the lower forms, es- 

 pecially those devoid of chlorophyl. Among these forms all gra- 

 dations may be found between aerobes and anaerobes, and some 

 of them may spend extended periods with, and without oxygen. 

 Some species have been demonstrated to be able to exist many 

 generations without access to free oxygen, but actual proof that 

 any organism is capable of indefinite life without this supply has 

 not been adduced, although it seems quite probable from all the 

 evidence at hand. Many of the anaerobic organisms are capable 

 not only of carrying on intramolecular respiration but also of 

 producing fermentation in a medium in which they live. Fer- 

 mentation may be due to the direct action of the protoplasm, or 

 to that of substances, enzymes, secreted by it. It may occur in 

 the tissues of the plant, or the enzyme may be excreted, and set 

 up disintegration in the medium in which the plant lies. The latter 

 is the case in nearly all of the simpler forms like bacteria and 

 fungi. Such fermentations may be accompanied with the evolu- 

 tion of carbon dioxide and other gases, or not, and are generally 

 characterized by an enormous liberation of energy, and some 

 heat. As pointed out in a previous paragraph, the fermentation 

 may be simply for the purpose of rendering substances assimil- 

 able and thus constitute digestion. 



326. Estimation of the Amount of Carbon Dioxide Given off and 

 Oxygen Absorbed During Respiration. Germinate about 200 cc. 

 of seeds of wheat, or corn, and when the roots are about 3 cm. 

 in length place in a suitable vessel and set in the receiver used 

 for the volumetric determination of the interchange of gases in 

 photosynthesis (Fig. 1 1 8). Insert a naked bulb thermometer in 

 the seeds, make the proper connections and determine the pro- 

 portion of carbon dioxide and oxygen present at the beginning 

 Of the test. Allow the preparation to stand for four hours and 



make a second estimation. If the capacity of the bell-jar cover- 

 18 



