30 or VITAL MOTION. 



and that no part is specially concerned in the process. 

 Each cell, as it would appear, aids in the production 

 of the general current; and this, therefore, is com- 

 pounded of an infinite number of minor currents. The 

 sap, indeed, may be said to rise as through a porous 

 rock ; and the analogy would be nearly perfect, if we 

 could imagine the component crystals to be hollow 

 and porous, and the stream to filter through their 

 cavities as well as in the interstices. That the leaves 

 or spongioles have no special power in determining 

 these movements, though at times these are tlie main 

 entrances to fluid, is evident from the changes in the 

 main current of the sap which take place in winter 

 and summer; for whatever function seems to belong 

 to the leaf at one time is transferred to the rootlet at 

 the other, so that the function of either, in relation to 

 the absorption or exhalation of fluid cannot be re- 

 garded as absolute. In the arguments, also, which 

 show the essential unity of the various parts of the 

 plant, which have been set forth elsewhere,* there is a 

 strong reason for the belief in the possibility of a 

 change of function in these parts. 



The entire subject however is very imperfect, and 

 many new observations must be made before it can 

 be fully known. At the same time, it is sufficiently 

 clear that the phenomena of the general circulation 



'- Proteus ; or, the Law of Nature." London : J. Churchill, 

 1850. Pages 9, &c. 



