NUTRITION, STORAGE, AND RESPIRATION 115 



carbohydrate, with carbon dioxide as one of the final consequences. 

 It may be readily demonstrated in germinating seeds excluded 

 from the air. 



If a few soaked and already germinating peas be passed up into an inverted 

 test-tube completely filled with mercury, care being taken to exclude any 

 bubbles of gas, after some hours gas will be found to have accumulated over 

 the mercury, and it will continue to increase for several days. On testing, 

 it will be recognised as carbon dioxide. This evolution of carbon dioxide 

 without any absorption of oxygen has been styled Intramolecular Respiration. 

 Organisms showing it may be described as anaerobic, as distinct from aerobic 

 organisms, which live exposed to the air. In the case of the peas it is an 

 abnormal condition, and life under these circumstances is not long maintained 

 in them. But there are many of the lower organisms which can exist inde- 

 finitely, and even normally in the absence of atmospheric air. They are 

 called anaerobic organisms, and the most familiar of them is the Common Yeast, 

 when actively carrying on fermentation at the bottom of a beer-vat. 



Respiration is necessary in -normal plants for active vitality, 

 just as much as it is for animals. Successful germination depends 

 upon it. Growth does not proceed without it. The movements, 

 whether of the protoplast or of various members, as in the Sensitive 

 Plant and others which sliow phenomena of movement, cease in the 

 absence of a supply of free oxygen. In fact respiration viay be 

 recognised as the normal means of liberating the energy which is required 

 for carrying on the vital processes of the organism. The absorption of 

 oxygen, and the liberation of carbon dioxide may appear to be simple 

 processes. But it is probable that these are only the first and last 

 steps in very complex metabolic changes. Speaking generally these 

 are changes of degradation : of breaking up of more complex molecules 

 into simpler ones ; these changes, like those of combustion, end in 

 carbon dioxide and water, together with an evolution of available 

 energy. 



It will be obvious that Photo-Synthesis and Respiration involve 

 opposite interchanges of gases ; and particularly that in the former 

 carbon is acquired from the atmosphere, while in the latter it is liberated. 

 By the former the supply of organic material is increased, by the latter 

 it is diminished. But the former goes on only under the influence of 

 light : the latter goes on constantly during life, independently of 

 light. Accordingly, while respiration only will proceed during the 

 night, both may proceed simultaneously during the daytime. It will 

 then depend upon the relative activity of the two processes whether 

 the plant gains on the whole, or loses in substance. It certainly loses 

 by respiration during the night, or if kept in the dark. The young 



