FOLIAGE LEAVES : THE LIGHT-RELATION 15 
relation is to be observed, therefore, between the length 
of leaves and their distance apart in the same vertical row. 
The same kind of relation can be observed in reference 
to the breadth of leaves, for if leaves are not only short but 
narrow they can stand very close together. It is thus seen 
that the length and breadth of leaves, the number of ver- 
tical rows on the stem, and the distance between the leaves 
FIG. 8. A dragon-tree, showing narrow leaves extending in all directions, and nuraer 
ous vertical rows. 
of any row, all have to do with the light-relation and are 
answers to the problem of shading. 
19. Elongation of the lower petioles. There is still 
another common arrangement by which an effective light- 
relation is secured by leaves which are broad and placed 
close together on the stem. In such a case the stalks 
(petioles) of the lower leaves become longer than those 
above and thus thrust their blades beyond the shadow (see 
Fig. 9). It may be noticed that it is very common to 
