598 CONSERVATIVE ORGANS. [LECT. X. 



obvious. In the stems of monocotyledons, the 

 vessels run nearly in straight lines in distinct fas- 

 ciculi, embedded in a cellular pulp; and a simi- 

 lar vascular arrangement presents itself in the 

 leaves of this tribe of plants. In dicotyledons, on 

 the other hand, the vascular fasciculi of the stem 

 are not distinct, but form a reticular tissue which 

 covers the whole circle of the stem ; and., in like 

 manner, in the leaves, the vessels ramify in every 

 direction, forming a most complicated and beau- 

 tiful network, the interstices of which are filled 

 with the cellular pulp. The leaf, therefore, may 

 be regarded., in some respects, as a mere expansion 

 of the stem; and, consequently, in aphyllous plants, 

 we perceive that the stem is adapted to perform all 

 the functions of the leaf. The internal structure 

 of the floral leaves or bractece, and of those more 

 temporary foliar appendages, which are termed 

 stipulce, is nearly the same as that of the real 

 leaf; even the scales that envelop buds, and which 

 are always described as deriving their origin from 

 the cortical part only of the stem, and consisting 

 chiefly of cellular matter, have in every respect 

 the same structure as leaves, as far, at least, as 

 relates to their vascular and cellular systems. 



