8o 



GROWTH AND WORK OF PLANTS 



petiole and then diverge something like the digits of the hand 

 (palm) toward the margin of the leaf, as in the maple. In 

 pinnate leaves there is a main vein which extends from 

 the petiole directly through the middle line of the leaf, and 

 the main branches from this arise at nearly right angles and run 

 nearly parallel toward the margin of the leaf, like the "veins' 7 

 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. 



125. 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 deter- 

 mination of species. Some of the 

 more general types may, however, be 

 mentioned.* There are two general 

 kinds, simple leaves and compound 

 leaves. 



126. Simple leaves. Simple 

 leaves are those which consist of a 

 single blade. The blade may be oval 

 in outline, or heart-shaped, elliptical, 

 lanceolate, arrow-shaped, reniform 

 (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 prominent teeth (dentate leaves), or with rounded 

 teeth when the margin is scalloped (crenate leaves), etc. When 



* Some of the greater variations are mentioned under modifications of 

 leaves (paragraphs 148-153). 



Fig. 70. 



