106 M. Dutrochet's Discoveries in Vegetable Physiology. 



This descent of the sap M. Dutrochet ascribes to a mutual in- 

 terchange (through the operation of endosmose) of the fluid 

 contents of the oblong cells, which give out through their sides 

 the nutritive matter contained in them. This is dissolved by 

 the first ascending sap in spring, and is carried up for the de- 

 velopement and formation of the fruit, and for the growth of 

 the stem. 



The sap of plants is likewise diffused laterally for the pur- 

 pose of nutrition and developement. This is effected by en- 

 dosmose, which produces the interchange in the fluids of the 

 cells already mentioned. 



From the facts now mentioned, and many others which we 

 cannot even notice, M. Dutrochet draws the following conclu- 

 sions. 



1. That in vegetables there is no circulation of sap, but 

 merely an ascending and a descending current, and a lateral 

 diffusion of the sap. 



2. That the sap ascends through cylindrical tubes passing 

 through both the alburnum and the old wood. 



3. That the juice elaborated in the leaves is conducted 

 through a set of oblong closed cells existing chiefly in the 

 bark. 



4. That the lateral diffusion of the sap and the elaborated 

 juice is effected through the organic membrane which forms the 

 cellular tissue. 



5. That these motions are the effects of distinct electrical cur- 

 rents, one, viz. endosmose, operating so as to introduce fluids 

 into the cells and capillary organs of the plant, and the other, 

 viz. exosmose, operating so as to abstract it from them. 



6. By endosmose the sap rises to the tops of trees contrary to 

 its natural gravity, and independent of any contractile power 

 in the vessels which contain it ; and, 



7. That secretion in plants, and consequently nutrition, de- 

 pend wholly on electrical agency. 



We shall now proceed to the later memoir of M. Dutrochet, 

 in which the preceding views are considerably extended, and 

 more firmly established. 



" When two fluids, says he, differing in density and in che- 

 mical properties are separated by a thin and permeable mem- 



