LECT. VII.] ANATOMY OF STEMS. 317 



pursuing our inquiries, we find that the bark is 

 readily detached from the wood, b. and is sepa- 

 rable into three layers ; that the wood is fibrous 

 and more compact and harder within than in its 

 exterior part ; and that the pith is evidently com- 

 posed of cells, which, ,in the more succulent parts 

 of the shoot, are filled with an aqueous fluid, and 

 in the drier with air. Such is nearly the sum of 

 the information we can obtain from an examina- 

 tion with the naked eye ; to secure, therefore, an 

 accurate knowledge of these parts, we must call 

 in the aid of the microscope ; and, with its as- 

 sistance, let us examine each of them in the order 

 in which they present themselves in the shoot 

 under our inspection, beginning with the bark. 

 In taking this course, we shall confine our actual 

 demonstrations to this shoot : pointing out, how- 

 ever, and illustrating as far as possible, the va- 

 rieties which have been remarked in each part, in 

 different ligneous stems, both in their first year's 

 growth, and in the after-periods of their ex- 

 istence. 



a. The BARK. In the shoot we are now ex- 

 amining, which has been cut in the autumn, the 

 bark when separated from the wood is about the 

 sixteenth part of an inch in thickness, and ap- 

 pears, to the naked eye, to be composed of four 

 very distinct parts. 1. A dry, leathery, fawn- 

 coloured, semi-transparent, tough membrane, 



