LEAVES 13 
The overlapped base is not expanded so much as the ex- 
posed apex, and hence such leaves are usually narrow 
toward the base and broad toward the apex. This nar- 
rowing at the base is sometimes carried so far that most 
of the overlapped part is only a petiole. 
(4) Leaf-mosaics.—All leaf adjustments (including the 
spiral arrangement, elongation of lower petioles, etc.) 
that have to do with fitting leaf-blades together, so that the 
greatest amount of leaf surface may be exposed to direct 
illumination, may be regarded as concerned in the con- 
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Fic. 9.—Leaves of Fittonia showing mosaic arrangement. 
struction of a leaf-mosaic. A general mosaic arrangement 
of leaves may be observed in connection with almost every 
broad-leaved plant (Figs. 8 and 9); and even when the 
leaves are separated along an erect stem, a view from above, 
