LEAVES, THEIR FORM AND MOVEMENT 73 



right angles and run nearly parallel toward the margin of the leaf, 

 like the " veins " in a feather or pinna. Examples are seen in 

 the oaks, apple, quince, beech, rubber plant, etc. Netted veined 

 leaves are characteristic of the dicotyledons. 



2. FORM OF LEAVES. 



120. Leaves vary greatly in form, not only as to the general 

 outline, but also as to the character of the margin and the division 

 of the blade. The multitude of these 



variations it would be out of place to 

 enumerate here, since a knowledge of 

 them is chiefly of value in descriptive 

 work and in the determination of species. 

 Some of the more general types may, 

 however, be mentioned. Some of the 

 more aberrant variations are mentioned 

 under modifications of leaves. There are 

 two general kinds, simple leaves and 

 compound leaves. 



121. Simple leaves. Simple leaves 

 are those which consist of a single blade. 



The blade may be oval in outline, or Fig 6? 



heart-shaped, elliptical, lanceolate, Leaf of Tropaeoium, a peltate 



' ' ' leaf with palmate venation. 



arrow-shaped, remform (kidney-shaped), 



etc., and the edge may be plain, or irregular when the margin may 

 have the appearance of being cut into minute teeth like the cutting 

 edge of a saw (serrate leaves), as in the apple, or with more promi- 

 nent teeth (dentate leaves), or with rounded teeth when the margin 

 is scalloped (crenate leaves), etc. When the divisions extend 

 deeper the leaf is cut, when nearly or quite halfway to the midrib 

 the leaf is lobed, when halfway or more cleft, when nearly to the 

 midrib parted, and when the divisions extend quite to the midrib 

 the leaf is divided. The margins of the lobes or divisions may then 

 be plane or serrate, etc. These divisions take place between the 

 more prominent veins so that the leaf may be pinnately lobed, 



