180 



PRACTICAL COURSE IN BOTANY 



Observe both branches in their natural position ; what part 

 of the leaf is turned upward, the edge or the surface of the 

 blade? Change the position of the two sprigs, placing the 

 vertically growing one horizontal, and the horizontal one 

 vertical. "What part of the leaves is turned upward in each ? 



232 233 



Figs. 232, 233. — Adjustment of leaves to different positions : 

 232, upright ; 233, procumbent. 



197. Leaf mosaics. — Trees with horizontal or drooping 

 branches, like the elm and beech, and vines growing along 

 walls or trailing on the ground, generally display their foliage 

 in flat, spreading layers, each leaf fit- 

 ting in between the interstices of the 

 others like the stones in a mosaic, 

 whence this has been called the mosaic 

 arrangement. (Plate 10.) In plants of 

 more upright or bunchy habit, the 

 leaves are placed at all angles, giving 

 the appearance of a rosette when viewed 

 from above, whence this is called the 

 rosette arrangement. 



A variety of the same disposition is 

 seen in the pyramidal shape assumed 

 by plants with large, undivided leaves 

 like the mullein and burdock (Fig. 237), in which access of 

 light is secured by a mutual adjustment between the size 

 and position of leaves, the upper ones becoming successively 

 smaller. 



Fig. 234. — Leaf mosaic 

 of olm. 



