RESPIRATION. 89 



rature it becomes slower, and ceases at the freezing 

 point of water. 



76. In regard to these motions seen to take place in 

 plants, an analogy has been drawn between them and 

 the circulation of the blood in animals, and were it not 

 that plants are destitute of a central system or organ 

 from which the moving fluids set out and to which they 

 return, as in the higher beings, (although it may be 

 maintained, as Schultz has done, that there are certain 

 foci to be demonstrated,) a considerable degree of pro- 

 probability might attach to the supposition. 



77. The difference between rotation and cyclosis is 

 differently marked by Schultz than in the forementioned 

 paragraphs, as he considers that rotation is never seen 

 in plants in which cyclosis is met with, and that it is 

 strictly confined to the lowest tribes ; and that what is 

 termed rotation in the others, is but a form of cyclosis 

 under peculiar modifications, and also that cyclosis is 

 not to be seen in the lowest orders of plants. 



78. The causes of the motions of rotation and cyclosis 

 are strictly vital ; electricity, galvanism, and contrac- 

 tions of solids, etc., all fail in its explanation, as even 

 acknowledged by non-vitalists of the day ; and the con- 

 clusion that we can only come to is that already ex- 

 pressed in paragraph 50, when speaking of the causes 

 of the motion of the crude sap. 



RESPIRATION. 



79. Essentially connected with the performance of 

 nutrition is the function we have now to speak of, 

 namely, that of respiration. We have seen under diges- 

 tion that by the decomposition of carbonic acid oxygen 

 is evolved by the leaves, and that its carbon is retained ; 

 in this process, on the other hand, oxygen is absorbed, 

 and carbonic acid is evolved. Until lately the evolution 

 of oxygen was considered as belonging to this function, 

 i 3 



