114 BOTANY AND PHARMACOGNOSY. 



shaped; connate-perfoliate, when opposite leaves are con- 

 nected at the base and surround the stem; perfoliate, when the 

 leaf simply clasps the stem. In Monocotyledons the base of the 

 leaf is frequently prolonged into a sheath, which may entirely 

 surround the stem, as in grasses, and is known as a ligule. 



Margin of Leaf. — Very few leaves of dicotyledonous plants 

 possess an even margin, and according to the degree and charac- 

 ter of the incisions or indentations they are described as serrate, 

 when the apex of the divisions or teeth is sharp and directed for- 

 ward like the teeth of a saw ; dentate, when the divisions project 

 outward; crenate, when the teeth are more or less rounded; 

 repand, when the margin is somewhat wavy ; sinuate, when the 

 wavy character is pronounced; lobed, when the incisions extend 

 not more than half-way into the lamina, and the sinus (or hollow) 

 and the lobe are more or less rounded ; cleft, when the incisions 

 are still deeper and the sinuses and lobes are somewhat acute; 

 and DIVIDED (Figs. 75 and J^^, when the incisions extend almost 

 to the midrib. 



Compound Leaves. — The divisions of a parted leaf may 

 assume the :form of a sirfiple leaf, when the divisions are known 

 as leaflets and the whole as a compound leaf. The distinction 

 between a simple leaf and a leaflet is, that the former has a bud in 

 the axil. The difference between the divisions of a simple leaf 

 and those of a compound leaf is this, — in the former they never 

 become detached from the petiole or midrib, whereas in the com- 

 pound leaf they are articulated and drop off individually. Com- 

 pound leaves may be divided into PiNNATELY-compound (Fig. 163, 

 ^) or PALMATELY-compound (Fig. 78, £), this distinction depend- 

 ing upon whether the leaflets are arranged pinnately or palmately. 

 A number of forms of pinnately-compound leaves are recognized. 

 When the leaflets are all lateral (Fig. 71) the leaf is said to be 

 pari-pinnate; when there is an odd or terminal leaflet as in 

 Sumac (Fig. 164) the leaf is impari-pinnate ; when the midrib 

 is prolonged into a tendril as in the garden-pea (Pisuni), the 

 leaf is said to be cirrhiferous-pinnate. 



Movements of Leaves. — The leaves as well as other organs 

 of plants exhibit a variety of movements or curvatures in response 

 to stimuli of different kinds, and are said to possess the property 



