LBCT. VII.] ANATOMY OF STEMS. 315 



liber, no alburnum, and no medullary rays; parts 

 which, as I shall soon have occasion to demon- 

 strate to you, belong, exclusively, to the dicoty- 

 ledonous and polycotyledonous stems. I do not, 

 at present, attempt to detail to you either the 

 opinions of others, or my own conjectures, re- 

 lative to the manner in which the various parts of 

 these stems are formed; nor to trace their par- 

 ticular functions ; as we shall enter fully into this 

 part of our subject, when we arrive at the proper 

 moment for taking into consideration the combined 

 functions of the root, stem, and leaves. 



iii. Stems belonging to plants, which are pro- 

 duced from dicotyledonous and polycotyledonous 

 seeds, are in every respect alike in point of struc- 

 ture ; and, therefore, for the sake of brevity, I 

 shall describe both under the single appellation of 

 Dicotyledonous stems. In treating of these, their 

 natural division into woody and herbaceous imme- 

 diately presents itself to our attention. 



A. WOODY DICOTYLEDONOUS STEMS consist of 

 three distinct parts, the bark, the wood, and the 

 pith. They are best exemplified in trees and 

 shrubs ; but as the structure of each of these parts 

 differs according to the age of the plant, it is re- 

 quisite to examine them, both as they appear in 

 the young plant or the shoot one year old only, 

 and in the trunk and branches of older subjects. 

 If the young shoot of any tree or shrub, the 



