202 



ELEMENTARY STUDIES IN BOTANY 



the rocks (Figs. 163 and 164). This close overlapping of 

 leaves is a very poor adjustment to light at best, but there 

 is evident an adjustment to secure the most light possible 

 under the circumstances. The lowest leaves of the rosette 

 are the longest, and the upper ones become gradually shorter, 

 so that each leaf has at least a part of its surface, and usually 

 the broadest part, exposed to light. 



FIG. 166. The leaf-mosaic of 



Fittonia; observe also the beautifully distinct 

 veining. 



All of these adjustments to light may be brought together 

 under the conception of a leaf-mosaic, by which is meant the 

 arrangement of leaf-blades with reference to one another so 

 that the greatest amount of leaf surface may be exposed to 

 direct illumination. A general mosaic arrangement of leaves 

 may be observed in connection with almost every broad- 

 leaved plant (Figs. 165 and 166) ; and even when the leaves 



