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- 



FIG. 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, 



