106 s ESSENTIALS OF BOTANY 
leafy twig, by a twisting about of the petioles. The adjust- 
ment in many opposite-leaved trees and shrubs consists 
in having each pair of leaves cover the spaces between 
the pair below it, and sometimes in 
the lengthening of the lower peti- 
oles so as to bring the blades of 
the lower leaves outside those of 
the upper leaves. Examination 
~ of Figs. 72 and 78 will make the 
matter clear. 
The student should not fail to 
study the leafage of several trees 
of different kinds on the growing 
tree itself, and in climbers on walls, 
and to notice how circumstances 
modify the position of the leaves. 
Maple leaves, for example, on the ends of the branches are 
arranged much like those of the horse-chestnut, but they 
are found to be arranged more nearly flatwise along the 
inner portions of the branches, 
that is, the portions nearer the 
tree. Figs. 74 and 75 show the 
remarkable difference in arrange- 
ment in different branches of the 
Deutzia, and equally interesting 
modifications may be found in 
alternate-leaved trees, such as sedi 
the elm and the cherry. Fic. 71. Leaf Arrangement 
125. Leaf-Mosaics.— In very Ore ebere rte 
many cases the leaves at the end of a shoot are so arranged 
as to form a rather symmetrical pattern, as in the horse- 
chestnut (Fig. 72). When this is sufficiently regular, 
Fic. 70. Leaf Arrangement 
of the Oak. 
