LEAF ADJUSTMENT 



4; 



55. Mosaics and Rosettes. — A very little observation 



will show that 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 



fitting in between the interstices 



of the others like the stones in a 



mosaic, whence this has been called 



the mosaic arrangement. In plants 



of more upright or bunchy habit, on 



the other hand, the leaves grow at 



all angles, with a general tendency to cluster in rosettes at 



the end of the branches, 

 as in the magnolia, horse- 

 chestnut, sweet gum, etc., 

 thus giving rise to what 

 is known as the rosette 

 arrangement. 





. — Leaf mosaic of elm. 



^^!*i£<^ 





89,90. — Horse-chestnut leaves: 89, leaf rosette seen from above; 90, the same 

 seen sidewise, showing the formation of rosettes by the lengthening of the lower 

 petioles. 



56. Leaf Cones and Pyramids. — These forms usually 

 result from a lengthening of the lower petioles to secure a 

 better light exposure for the under leaves, or from an 

 increase in the size of the leaves themselves, as we see in 

 the rosettes that form about the roots of our common 

 biennial and perennial herbs in winter. To the same 



