,22 PLANT PHYSIOLOGY 



5. RESPIRATION (ENERGESIS) AND FERMEN- 

 TATION. 



We have now traced the formation of the basal organic sub- 

 stances and their transformation, or conversion, into the prin- 

 cipal of the multitudinous special materials displayed by plants. 

 But these are not immortal, and sooner or later they vanish. 

 We must now trace their fate, which in general lies in one of 

 three directions. First they are absorbed by animals, or by 

 parasitic plants, of whose tissues they become a part. Second 

 they decay by chemical and physical methods to be noted below. 

 Third they disappear by an important process with which the 

 student has probably already come into contact under an earlier 

 suggested experiment (page 95). That experiment implied 

 a loss of weight in growing tissues when photosynthesis is not in 

 progress; and it is very easy, by experiments along the line of 

 that suggested, or by others of like sort which the student may 

 readily devise for himself, to prove that, excluding photosynthe- 

 sis or other addition of substance, this loss of weight is universal 

 in all living organisms where work of any kind, including even 

 the bare maintenance of life, is in progress. Since, however, 

 as the principle of the conservation of matter teaches, the van- 

 ishing material cannot be obliterated, its only possible fate would 

 appear to be its escape in the form of a gas. Such a possibility 

 entails far-reaching consequences, and hence calls for experi- 

 mental study, thus presenting the problem: 



Is any gas released by working tissues of plants, and if so, 

 what is its identity? 



This may be determined very readily by a test of the gas in a cham- 

 ber in which working tissues have been kept for some time. 



EXPERIMENT. Into the chamber of a respiroscope insert germi- 

 nating oats or barley in suitable quantity, and stand the open end in 

 a small dish of mercury; give favorable conditions for germination 

 in darkness for two days, then apply tests for the gases present, begin- 

 ning as usual with that for carbon dioxide (page 98). 



PRECAUTIONS. While the seeds will germinate in the chamber if well 

 soaked, it is practically best to germinate them first, in a saucer germinator, 



