LECT. VII.] ANATOMY OF STEMS. 291 



those stems which are the simplest, because com- 

 posed of the fewest parts ; and progressively pre- 

 pares us to understand the organization of those 

 of a more compound nature. I shall, therefore, 

 attempt such an arrangement, and class stems, 

 in reference to their anatomical structure, into 

 the three following divisions : 



i. Stems which display, internally, an appa- 

 rently homogeneous mass. 



ii. Stems which proceed from monocotyledonous 

 seeds. 



iii. Stems which proceed from dicotyledonous 

 and polycotyledonous seeds. 



i. Stems which display, internally, an apparently 

 homogeneous mass, when examined by the unassisted 

 eye, seem to consist simply of an epidermis enclos- 

 ing a parenchyma, composed either of cellular 

 substance, of very different degrees of succulency, 

 sponginess, dryness, and density ; or of inter- 

 woven fibres, forming a leathery, or a felt-like tex- 

 ture, or one not a little resembling that of washed 

 animal muscle which has been macerated in spi- 

 rits. When examined, however, by the aid of a 

 good microscope, these different appearances of 

 the internal mass are all found to consist of cel- 

 lular substance, with vessels running through 

 it, and anastomosing in a variety of directions. 

 Mirbel erroneously asserts that this description of 



