64 



TRANSFORMATIONS OF THE LEAF. 



304. The scales which clothe the various forms of scale-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 

 are fleshy, serving as depositories 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. 



305. Bud scales. The brown scales which cover winter buds are of 

 the same nature and origin. 



306. The cotyledons of seeds or seed-lobes are readily recognized 

 as leaves, especially when they arise above ground in germination, and 

 form the first pair upon the young plant, as in the beech-nut and squash 

 seed. Their deformity is due to the starchy deposits with which they 

 are crammed for the nourishment of the embryo when germinating, 

 and also to the way in which they are packed in the seed. 



307. Phyllodia are certain leaf-forms, consisting of petioles exces- 

 sively 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. 



174 175 176 177 



Ascidia. 173, Nepenthes. 174, Sarracenia psittacina. 175, S. purpurea. 176, S. Gronovii, /J. 

 Druinmondii. 177, Acacia keterophylla, its phyllodia. 



308. Ascidia or pitchers, are surprising forms of leaves, expressly contrived, as 

 if by art, for holding water. The pitchers of Sarracenia, whose several species are 

 common in bogs North and South, are evidently formed by the blending of the in- 

 volute margins of the broadly winged petioles, so as to form a complete vase. The 

 broad expansion which appears at the top may be regarded as the lamina. These 

 pitchers contain water, in which insects are drowned, being prevented from escap- 

 ing by tho deflexed hairs at the mouth. 



