274 DECOMPOSITE ORGANS. CHAP. I. 



fibres, and the veins of the smaller bundles. In 

 simple leaves, whether entire or indented, whether 

 petiolate or sessile, the fibres of the petiole or base 

 branch out into several large and principal nerves 

 expanding like the ribs of a fan, and diminishing 

 in size as they elongate by means of the ramifica- 

 tions they send out, till they are at last lost in the 

 margins. There are examples, however, in which 

 the fibres or nerves of the expansion project beyond 

 the margin, and hang down in the form of threads, 

 as well as others in which they fall short of the 

 margin, the leaf being bounded by a thin and mem- 

 branaceous border that seems to be merely a prolon- 

 gation of the epidermis. 



Sometimes three or more of the principal nerves, 

 as in Narrow-leaved Plantain, take rather a vertical 

 * direction, and extend from the base to the apex of 

 the expansion. But in leaves that are lobed or 

 divided, the division is always formed by a princi- 

 pal nerve proportioned to the size of the lobe. The 

 form of the expansion therefore depends upon the 

 peculiar mode of ramification assumed by the fibres 

 after quitting the petiole. In the Grasses, indeed, 

 the distinction of the fibres of the petiole or sheath 

 investing the stem is already analogous to that of 

 the expansion of the leaf, except that the bundles 

 or nerves are fewer in the former than the latter, 

 branching out into minuter divisions as they ascend 

 obliquely from the one into the other. 

 Which But the circumstance which is the most singu- 



eonsists of 



two, * 



