116 



MORPHOLOGY OF LEAVES. 



decisive instance of leaves used for storage of food is in that 

 material provision for the nourishment of the embryo in germi- 

 nation, in which the first leaves, the cotyledons, are turned to this 

 account. (21-37, &c.) After or 

 while discharging this special duty, 

 the cotyledons may fulfil their gen- 

 eral office, by serving as foliage (as 

 in Maples, Fig. 8, and Pumpkins, 

 Fig. 47) ; or, through various inter- 

 mediate conditions, they may be 

 wholly devoted to storage, as in 

 'the Pea, Oak, Horsechestnut, &c. 

 (Fig. 37-43.) 



226. Leaves as Bulb-scales, how- 

 ever, are for the most part wholly 

 applied to this use, being leaves 

 reduced to short scales or to 

 concentric coats, and thickened 

 throughout by nutritive deposit. 

 The accumulation of such leaves 

 forms the mass of the bulb, as of 

 the Lily, Fig. 118, Onion, Fig. 

 113, &c., also of bulblets. (120.) 



227. Leaves as Bud-scales, being 

 for protection of nascent parts, have 

 been explained under buds. (70.) 

 The evidence of foliar nature af- 

 forded by transition is well exhib- 

 ited by the Sweet Bucke} r e, although 

 the whole series of gradations, from 

 bud-scales to compound leaves, 

 is seldom seen united in one bud, 

 as in Fig. 233. In this case, the 

 bud-scales are homologous with 

 petioles. In Magnolia, they consist 

 of stipules (Fig. 81, 82) : in the 



Lilac, they are homologous with leaf-blades. The two pairs of 

 bud-scales which subtend and protect through winter the nascent 

 head of flowers of Cornus florida are morphologically the apex of 



centrated condition, in the form of a solid grain, which remains for next 

 year's use, the whole leaf except this thickened base dying away at the close 

 of the short season's growth. 



FIG 233. Leaves of a developing bud of the Low Sweet Buckeye (^Esculns parvi- 

 flora), showing a nearly complete set of gradations from a scale to a compound leaf o\ 

 five leaflets. 



