LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 413 



leaves decay and fall in autumn, the function of 

 the fibrils being no longer required, they also decay 

 and separate from the radicles ; but in evergreen 

 shrubs, the office of the leaves being permanent, 

 the new set always appearing before the old set 

 falls, the continued presence of the fibrils becomes 

 also requisite. 



Such is the root of ligneous dicotyledons. Its 

 similitude both in structure and functions to the 

 portion of the tree above ground is very obvious, 

 the caudex resembling the stem, the radicles the 

 branches, and the fibrils the leaves ; *and hence 

 trees have been inverted and yet have lived ; the 

 buried stein and branches being converted into 

 roots, whilst the roots elevated into the air and 

 light have assumed the characters and performed 

 all the functions of the organs, the place of which 

 they now supply. 



B. HERBACEOUS DICOTYLEDONOUS STEMS are so 

 much diversified in structure, particularly as far 

 as relates to the arrangement of the parts, that it 

 is impossible to form as accurate an idea of their 

 anatomy from the examination of one or two spe- 

 cimens, as we are enabled to do of that of the 

 stems of dicotyledons. To obviate, however, in 

 some degree, this objection, I shall divide them into 

 two classes, comprehending under the first A. those 

 which have no central cavity^ or are entire, and 



