0(3 VEGETABLE ORGANOGRAPHY, 



Section VI. 



On the Physiological Function of the Cellules and 

 Intercellular Passages. 



The physiological function of the cellules is a subject 

 entirely belonging to Physiology, and one which we can 

 only here examine in a very brief way, and solely in an 

 incidental manner. 



The cellules, being closed on all sides, can only receive 

 the sap by means of the hygroscopicity of their walls. 

 Those which are round suck up the juices which sur- 

 round them, and elaborate them in their interior : and 

 it is thus that, by a vital process, they form the feculent 

 and mucilaginous substances, and the resinous matter 

 which gives them their colour. We also see these dif- 

 ferent substances abound in all parts of plants which are 

 essentially composed of round cellules ; as the paren- 

 chyma of the external covering of leaves and fruits, the 

 pith and the receptacles of flowers, &c. 



As to the elongated cellules which surround the 

 vessels, the part they perform is very difficult to com- 

 prehend : one never finds there the substances which 

 We have noticed ; and, for the most part, they appear 

 empty, or else filled with air, and in consequence par- 

 ticipate in the function of the vessels. 



The intercellular passages are generally full of sap, 

 and it is very probable that they are the parts which 

 serve essentially to its progress. We can, in this point 

 of view, divide them into three classes : — 



1st. The intercellular passages, situated between the 

 elongated cellules which surround the vessels, appear to 



