TKANSFGKMATIONS OF THE LEAF. 



107 



stems are leaves, or more usually petioles, reduced and distorted, 

 perhaps by the straitened circumstances of their underground 

 growth. The scales of corms and rhizomas are mostly mere 

 membranes, while those of the bulb arc fleshy, serving as deposi- 

 tories of food for the future use of the plant. That these scales 

 are leaves is evident 1st, from their position at the nodes of the 

 stem ; 2d, from their occasional development into true leaves. 

 Of the same nature arc the brown scales of Winter buds. 



320. The cotyledons of seeds or seed-lobes are readily recog- 

 nized as leaves, especially when they arise above-ground in ger- 

 mination, and form the first pair upon the young plant ; as in 

 the Beechnut and Squash seed. Their deformity is due to the 

 starchy deposits with which they are crammed for the nourish- 

 ment of the embryo when germinating, and also to the way in 

 which they are packed in the ssed. 



.4.v.-i, li.t. 391, Nepenthes. 302, Sarracpnia psittacina. 393, S. purpiiren. 391, S. Or uovii, Q. Drui 1 

 iiumdii. 395, Acacia heterophy Ha its phyllodia. 



321. Phyllodia are certain leaf-forms, consisting of petiole i 

 excessively compressed, or expanded vertically into margins 

 while the true lamina is partly or entirely suppressed. Fine 

 examples are seen in our greenhouse Acacias from Australia. 

 Their vertical or edgewise position readily distinguishes them 

 from true leaves. 



322. Ascidia, or pitchers, are surprising forms of leaves, ex- 



