552 CONSERVATIVE ORGANS. [LECT. X. 



stem contain a fine spiral fibre; which, however, 

 I have not been able to discover. 



Proceeding to the next division of plants, those 

 produced from monocotyledonous seeds, we ob- 

 serve the costae or vascular fasciculi distinguishable 

 by the naked eye; of different sizes, and running 

 in gently curved or nearly straight lines, either 

 from the base to the apex, or transversely from the 

 midrib to the margin of the leaf. The former is 

 found chiefly in those leaves which have no de- 

 cided 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 candi- 

 dum, may be taken as an example of the general 

 distribution and character of the vascular system 

 in the first description, the sessile leaves of mono- 

 cotyledonous plants. On examining it, we find that 

 the vascular framework consists of a distinct 

 midrib, which forms the keel of the leaf, and of 

 less elevated ribs (costce), that extend on each 

 side of the midrib in longitudinal lines, which 

 form a gentle curve, following the shape of the 

 leaf. In the smoother and more succulent leaves 

 of this division, however, these costae are scarcely 

 visible externally, or at least appear merely as 

 striae on the surface of the leaf: and this is the 

 case, also, as far as regards many of the smaller 

 vascular fasciculi, even in those leaves, which have 



