AS BUD-SCALES, TENDRILS, SPINES, ETC. 



167 



double purpose, being not only organs for assimilation, — the general 

 office of foliage, — but also repositories in whicli 

 assimilated matter is stored up, just as in the root 

 of the Beet and Radish (Fig. 138), or in subter- 

 ranean stems or branches in rootstocks, tubers, 

 and corms (188-190, 194). The bases of those 

 leaves wliich form the scales of bulbs (191) are 

 turned to the same use. In Fig. 176 we have a 

 leaf the blade of which acts as foliage in the ordi- 

 nary manner of leaves, while its subterranean 

 thickened base serves as a repository of nutri- 

 ment which the blade has elaborated. The very 

 first leaves of the plant, viz. the cotyledons or 

 seed-leaves (120-123) are commonly subservi- 

 ent to this purpose, and some- 

 times to no other, as in the 

 Pea, Horsechestnut, Oak, &c. 

 (124), where these leaves are mere repositories 

 of food for the use of the germinating plant. 



298. Leaves as Bud-scales, &c. (161) exhibit the 



same organ under a different modification, and 

 subserving a different special purpose. Of the 

 same nature are the degenerated or abortive 

 scale-like leaves on the vernal stems of peren- 

 nial herbs near or beneath the surface of the 

 ground, and on Asparagus shoots, and also those 

 scales which colored parasitic plants produce in 

 place of foliage (152). The primary leaves of 

 Pines are all thin and dry bud-scales ; the actual 

 foliage originating from a branch in the axil of 

 each (Fig. 212). 



299. leaves as Tendrils are seen in the proper 

 Pea tribe ; where however only the extremity 

 of the common petiole is transformed in this 



2S6 manner (Fig. 287, 289) ; but in one plant 



of the kind (Lathyrus Aphaca) the whole leaf becomes a tendril. 

 300. Leaves as Spines occur in several plants. The primary leaves 



FIG. 295. A twig of American Arbor Vita, ezliibifcing both awl-shaped and scale-shaped 



FIG. 296. A summer shoot of the Barberry, showing a lower leaf in the normal state ; the 

 next partially, those still higher completely, transformed into spines. 



