438 CONSERVATIVE ORGANS. [>ECT. VIII. 



verse slits; and the radiated cells are tubular 

 and arranged in symmetrical order. The cha- 

 racter of the proper vessels can scarcely be made 

 out, owing to their transparency and the white 

 juice with which they are filled; but they are evi- 

 dently perforated and communicate laterally with 

 the tubular cells, into which the juice they convey 

 is filtered, to be preserved for the purposes of 

 the plant. This juice probably undergoes some 

 change in its passage, as it appears to be more pel- 

 lucid in the tubular cells, than in the proper 

 vessels. 



As the root advances in age, additional vessels 

 are added to the fasciculi of sap vessels, until the 

 whole of the central part of the stem is nearly oc- 

 cupied with them ; and, the original cellular matter 

 being closely compressed between the fasciculi, 

 the vascular portion assumes the aspect of one 

 large fasciculus. Vessels are added exteriorly also ; 

 but these are much fewer in number, although 

 they are larger and more distinct than those within 

 the original circle. In the same manner a new 

 layer of cellular tubes and of proper vessels is an- 

 nually added to the bark, so that a transverse 

 section of an old root appears to the naked eye to 

 consist of an opaque woody central part sur- 

 rounded with concentric circles, alternately 

 opaque and transparent. The old cuticle, with a 

 portion of cellular matter adhering to it, is annu- 

 ally pushed outwards, as in the trunks of trees, 



