NATURE OF PLANTS 27 



by what devices the leaves are brought into the light. Especially 

 instructive are the leaf arrangements of plants growing in win- 

 dows or creeping over trellises, etc., where complicated twisting 



FIG. 16. Leaf rosette of evening primrose. Each leaf blade has a longer 

 petiole than the one above it, so that the leaves are not shaded by one 

 another. 



and elongation of stems and petioles are necessary to adjust the 

 leaves to the one-sided illumination. The angular leaves of some 

 begonias furnish excellent illustrations of this. Perhaps so many 

 plants bear angular leaves because they can be better adjusted 



FIG. 17. Leaf of Aralia. Note the angular shape of the leaflets and the 

 smaller ones filling the space between the larger ones. 



and fitted together without loss of space than would be the case 

 in rounded leaves, and smaller leaves can also be more advan- 

 tageously introduced between the larger ones (Fig. 17). The 



