420 The Physiology of Plants BOOK in 



textbooks of the time. Correct ideas began to make their 

 way again into favour with the appearance of the Experi- 

 mental-physiologie of Sachs in 1865 and the marshalling and 

 interpretation of the facts concerning respiration constitutes 

 by no means the least of his contributions to the physiology 

 of plants. He stated his views more fully in his Lehrbuch 

 (1868), in which he said that respiration consists as in animals 

 of the continual absorption of atmospheric oxygen into the 

 tissues, where it causes oxidation of the assimilated sub- 

 stances, and other chemical changes resulting from this. 

 He pointed out that the formation and exhalation of carbon 

 dioxide may always be observed, and he held that the 

 carbon may be attributed to the decomposition of organic 

 compounds. 



Sachs further showed that the activity of growth and of 

 metabolic changes is accompanied by increased activity of 

 the true respiratory processes, and held that the latter 

 take place everywhere so long as life exists. He pointed 

 out that the streaming of protoplasm and the movements 

 of periodically motile and irritable organs are lost in the 

 absence of a supply of oxygen. He also called attention 

 to the loss of weight met with during any suspension of 

 the nutrition and associated it with respiration. Not the 

 least important of his statements was that, while respiration 

 is a source of loss of substance, it is also in addition the 

 perpetual source from which flow the forces necessary to 

 the internal movements. Though he did not state it so 

 explicitly as writers who succeeded him, we can see here 

 an appreciation of the part this process plays in the energy 

 relations of the plant. 



Respiration after its re-establishment as a separate vital 

 process came to be regarded as a sort of combustion, in 

 which various constituents of the plant's food or of pro- 

 ducts of its metabolism, were in a way burnt away with 

 the formation of carbon dioxide. The entering oxygen 



