284 ANATOMY OF LEAVES. 



chantia pohjm,o?-pha, we find that the surface of the 

 lobes oi the leai-likc frond, when examined by an or- 

 dinary lens, is reticulated by depressed lines, within 

 es'h of which a small nipple-like body rises. When 

 a thin slice of a lobe is placed under the microscope, 

 these lines are discovered to be occasioned by vessels 

 which run immediately under the cuticle, anastomos- 

 ing with one another. This vascular net-work is form- 

 ed by a single porous tube, branching and anastomos- 

 ing so as to form irregular, lozenge-shaped meshes, 

 which are filled with a dark-green cellular parenchy- 

 ma. The vessel itself is closely connected with the 

 cellular matter, and when separated, bears the marks 

 of the cells on its sides. We find nearly the same vascu- 

 lar structure in the Mosses. The leaves of all the Moss- 

 es are sessile, although many of them are sheathing ; 

 and most of them are furnished with a midrib ; but 

 their minuteness prevents any certain information be- 

 ing obtained as to the manner in which the leaves re- 

 ceive their vessels from the stem, or whether there be 

 a distinct set of returning vessels : they appear to be 

 merely a continuation of the vessels of the cortex of 

 the stem. 



Proceeding to the next division of plants, those pro- 

 duced from monocotyhdonovs seeds, we observe the 

 costa? or vascular fasciculi distinguishable by the nak- 

 ed eye ; of different sizes, and running in gently curv- 

 ed or nearly straight lines, either from the base to the 

 apex, or transverely from the midrib to the margin of 

 the leaf. The former is found chiefly in those leaves 

 which have no decided petiole, but spring directly 

 from a bulb or a tuber ; the latter in those which are 

 petiolated. We shall examine each kind separately. 



A bulb leaf of the White Lily (Lilium candidum), 

 may be taken as an example of the general distribu- 

 tion and character of the vascular system in the first 



