LESSONS IN BOTANY. 209 



blade, the leaf is parted. If the divisions extend to the midrib, 

 or petiole, the leaf is said to be divided. 



In studying leaves it will be noticed that the lobes, divisions, 

 etc., correspond to the veining of the leaf, the veins and divisions 

 in some cases radiating from the base of the leaf blade, when they 

 are said to be palmately veined, lobed, parted, etc., as in the 

 maple leaf; in other cases the branching, lobes and divisions are 

 related to the midrib rather than to the base of the leaf, when it 

 is said to be pinnately veined, lobed, parted, etc., as in the leaves 

 of the oak. 



When a leaf consists of two or more parts, each part with a 

 distinct petiole, joined to the midrib or common petiole, it is a 

 compound leaf. It is often difficult to determine whether a leaf 

 is compound or simply divided. Leaves may be palma tely com- 

 pound, as in the case of the horsechestnut, or pinnately com- 

 pound, as in the case of the locust and pea. 



A pinnately compound leaf may terminate with a single leaflet, 

 a pair of leaflets, or a tendril. The leaflets of compound leaves 

 may be divided and subdivided, and the leaf be bipinnate or tri- 

 pinnately compound, or twice palmate, etc. 



Sometimes the stem grows through the base of the leaf, when 

 the leaf is called perfoliate. Sometimes two opposite leaves seem 

 to have grown together at the base, forming one roundish leaf 

 with the stem through the center. Such leaves are said to be 

 connate-perfoliate. 



Many leaves are nearly horizontal with an upper and lower 

 side. Many others are nearly vertical, having inner and outer 

 surfaces, as the leaves of the iris. An examination of the leaves 

 of the iris shows the older straddling over the younger, as a man 

 straddles a horse, hence the leaves are called equitant leaves. 

 Equitant leaves, and many others, have no distinction of petiole 

 and blade, as the lea.ves of the pine, spruce and juniper. The 

 stipules are sometimes large and conspicuous, as in the case of 

 the pea and clover. Sometimes they form a sheath around the 

 stem, as in some grasses, where they serve as petioles. 



Leaves sometimes take the form of cups, as in the pitcher 

 L. s.u 



