ANATOMY AND PHYSIOLOGY OF PLANTS. 223 



in celandine, in pncconn, and many others. It is red in patience 

 dock, and green in the periwinkle. The substance of the proper 

 juice is gummy in the cherry, plum and peach ; it is resinous in the 

 fir and juniper, and pine ; it is the astringent principle of the oak 

 and willow ; the aromatic oil of the cinnamon, and so on, with a 

 variety of plants. 



1C. To draw out a general view of what we have 

 said on the vascular system, it seems there are, in fact, 

 but two sets of vessels the common or sap-vessels of the 

 interior parts, and the proper or entire vessels of the bark. 



Many illustrative experiments have been made to discover the 

 actual function of each set, the results of which very faithfully prove, 

 that the sap or nutrient fluids of the plant are conveyed by the 

 common vessels to the leaves, where the superabundant watery 

 portions are exhaled, and the remaining juice altered in its nature 

 by their organization, and conveyed by an appropriate apparatus, 

 into the proper vessels of the bark. The common vessels, therefore, 

 may be considered as the ascending vessels, and the proper vessels 

 as the descending. This course of the fluids is further proved, by the 

 sap always being found ascending in the spring, and descending in 

 the autumn, and by there being no kind of communication with the 

 vessels of the bark and of the centre. 



GLANDULAR TEXTURE, ETC. 



17. In addition to the membranous, cellular, and 

 vascular structures and epidermis, there are also glan- 

 dular, ligneous, and other textures, which are sometimes 

 enumerated as solid components of the vegetable organi- 

 zation. Their names are sufficient to imply their struc- 

 ture and general functions. 



THE EPIDERMIS. 



18. In animals, we find there is an exterior covering 



