28 



LOBING OF LEAVES 



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. 1 6. 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 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 

 lobing and branching of leaves has become a characteristic of 



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

 smaller ones filling the space between the larger ones. 



many plants because such variations permit the illumination of 

 a larger leaf surface. This is particularly noticeable in our oaks 

 where the outer leaves are often deeply lobed, thus permitting 

 considerable light to pass through to the underlying leaves. Ob- 



