EXPOSURE TO LIGHT 237 
the notches may be very deep and divide the blade into lobes, as 
the leaves of the Gooseberry, Cotton, Dandelion, some Oaks, 
Maples, and many other plants illustrate. In some cases the 
blade is so divided that it is made up of independent portions 
united to a common stalk, each independent portion being called 
a leaflet. Many familiar plants, such as Clover, Alfalfa, Vetches, 
Fic. 219.— A, Margins of leaves. a, serrate; 6, dentate; c, crenate; 
d, undulate; e, sinuate. B, lobed leaf of Grape. C, pinnately compound 
leaf of Black Locust. A, after Gray. 
the Walnut, Ash, Locust, and Sumach, have leaves divided into 
leaflets. The number of leaflets into which the leaves of different 
plants are divided varies widely. In the leaves of Clover and 
Alfalfa three leaflets are common, while leaves of the Black 
Walnut often have twenty or more leaflets. (Fig. 220.) Leaves 
divided into leaflets are said to be compound, while those less 
divided are called simple. 
Leaflets resemble simple leaves and in case of some compound 
leaves it is possible for one to mistake the axis to which the leaf- 
lets are attached for a branch of the stem and the leaflets for 
leaves. However, since buds occur only in the axils of leaves, 
one can tell whether the leaf-like structure is a leaf or a leaflet 
by the presence or absence of a bud in its axil. 
Exposure to Light. — Unless the leaf is properly exposed to 
light, it can not be an efficient food-maker. It is not always a 
problem of securing enough light, but often one of escaping light 
that is too intense; for too intense light often injures leaves and 
consequently checks them in their work. The adjustment to 
