156 DEFICIENCY OF FLESHY STRUCTURE. 



out. Thus the Cochlearia, or Horse-radish, has the edges of 



its leaves nearly smooth, 

 when growing in a suffi- 

 ciently rich soil ; but if 

 starved, the blade will be 

 divided into separate 

 strips like the teeth of a 



d ( ^ ' \ K / HiX " comb, from the deficiency 



of flesh to fill up the spaces 

 between the veins. In the 

 accompanying figure are 

 represented the outlines 

 of different leaves, having 

 the same general distri- 

 bution of the veins, but a 

 different proportion of the 

 fleshy substances between 

 them. 



236. In some plants, 

 in which the framework of 



FIG. 64. DIFFERENT FORMS OF LEAVES HAVING the leaves is Very strong, 



THE SAME VENATION; a, Water Crowfoot; b, ,, , f .. . 



Jatropha ; c, Passion-flower ; d, Sterculia platani- tne eucls ot this project 



folia ; /, Dichondra ; g, Asarabacca. f rom tne e d ges of the leaf, 



when the latter is stunted in its development, forming sharp 

 prickles. This is the case in the Holly ; the prickles on the 

 leaves of which will be at once seen, if examined, to be simply 

 the dried and projecting terminations of the veins. On looking 

 at any full-grown Holly, considerable variety will be noticed in 

 the degree, in which the leaves have this prickly character ; and 

 in general it is seen, that the lower ones are the most stunted 

 and rough, whilst the upper ones have the parenchyma of the 

 leaf so much developed, as to include these extremities, and thus 

 to render the edges of the leaf quite smooth. Sometimes it has 

 been observed that a Holly, growing in a very luxuriant soil, 

 has had all its leaves in this manner metamorphosed, so as 

 entirely to lose the peculiar aspect of the tree. This is one of 



