LECT. VII.] THE STEM. 285 



It is now my object to direct your attention to 

 these differences, and to point out to you the cir- 

 cumstances in which they consist. 



If we take a number of stems and branches of 

 different kinds of plants, and cut, or break, or 

 tear them transversely and longitudinally; we 

 shall find that some of them are easily divided, 

 whilst others resist almost all our efforts ; that 

 some are moist, succulent, and fleshy; others 

 fibrous, spongy, and dry ; and others again formed 

 of both succulent and dry parts ; the latter pos- 

 sessing very different degrees of compactness, in- 

 duration, and tenacity. But, however considerable 

 these differences may appear, the more we investi- 

 gate the subject the more we shall be convinced, 

 that, as far as respects substance, the stems and 

 branches of the whole of the vegetable kingdom 

 may be arranged under two classes, the Woody 

 and the Herbaceous. 



A. WOODY stems (Caules lignosi) are those 

 which contain a very large proportion of ligneous 

 fibre ; or in which wood forms comparatively the 

 greater part of their bulk. It is found either in 

 threads or bundles which run longitudinally from 

 the base to the summit of the stem ; or is united 

 in one mass, formed of concentric circles, which 

 cohere and compress each other nearly from the 

 centre to the surface of the stem : the tribe of 



