FOLIAGE LEAVES. 



389 



in holding it in the expanded position. The mechanical tissue in the 

 framework alone could not support the leaf. Turgescence of the meso- 

 phyll is needed in addition. 



757. Cut or lobed leaves. In many leaves, the indentations 

 on the margin are few and 



deep. Such leaves pre- 

 sent several lobes the pro- 

 portionate size of which 

 is dependent upon the 

 depth of the indentation 

 or "incision." Several 

 of the maples, oaks, 

 birches, the poison ivy, 

 thistles, the dandelion, 

 etc., have lobed leaves. 

 Where the indentation 

 reaches to or very near 

 the midrib the leaf is 

 said to be cut. A study 

 of various leaves will 

 show all gradations from 

 simple leaves with plane edges to those which are cut or divided, as 

 in compound leaves, and the lobes are often variously indented. 



758. Divided, or compound leaves. The rose, sumac, elder, 

 hickory, walnut, locust, pea, clover, American creeper, etc., are 

 examples of divided or compound leaves. The former are pin- 

 nately compound, and the latter are palmately compound. The 

 leaf of the honey-locust is twice pinnately compound or bipin- 

 nate, and some are three times pinnately compound.* It is 



* Some of the different terms used to express the kinds of compound 

 leaves are as follows: 



Unifoliate (for a single leaflet, as in orange and lemon where the com- 

 pound leaf is greatly reduced and consists of one pinna attached to the 

 petiole by a joint). Bifoliate for one with two leaflets; trifoliate for one 

 with three leaflets, as in the clover; plurifoliate for many leaflets. Odd 

 pinnate for a pinnate leaf with one or more pairs of leaflets and one odd 

 leaflet at the end. 



Fig. 433- 

 Lobed leaves of oak forming a mosaic. 



