LECT. VII.] ANATOMY OF STEMS. 325 



any confidence is to be placed in the microscope, 

 there can be no doubt of the existence of the cel- 

 lular pores. That many of the cells, however, are 

 filled with minute particles, is perfectly evident ; 

 and the number of these is always greater where a 

 branch is given off. Their use is yet unascertained, 

 but it is not improbable that they are of a nutri- 

 tive nature, and deposited in the cells to be dis- 

 solved by the ascending sap for the evolution of 

 new parts. Independent of these particles, the 

 cellular integument is filled both with coloured 

 and colourless secreted juices ; and it is very pro- 

 bable that this part performs some changes on the 

 sap thrown into its cells, similar to those effected 

 in the leaf. 



The cellular integument is partially destroyed, 

 and reproduced, a great part of the old portion 

 being pushed outwards with the cuticle which 

 is annually detached ; while new cells are added 

 to that which remains at the time the new cuticle 

 is produced. 



3. Vascular layer. Imbedded in the cellular 

 integument and impinging on the internal sur- 

 face of the bark, are distinct bundles of entire 

 vessels, each of which is so arranged as to pre- 

 sent, in the transverse section of the stem under 

 consideration, a semilunar aspect * ; and, in the 



* Vide Plate 6, fig. 2, d. 

 Y3 



