LEAVES 



71 



function which the leaf may serva Leaves may be divided on 

 basis of venation into net-veined, in which the veins interlace, 

 and parallel-veined, in which the primary veins run more or 

 less parallel ( Fig. 49 ). The net-veined are of two types, those in 

 which the secondary veins arise from the mid-rib and are known 

 as pinnately veined (Fig. 49) and those which have three, five, 

 seven or nine primary veins or mid-ribs giving rise to the sec- 



FIG. 49. Typical net-veined leaf and typical 

 parallel-veined leaf. 



FIG. 50. Stipules of clover and 

 grass leaves. 



ondaries (Figs. 51 and 52). The parallel-veined are also of two 

 types, those in which the primaries run from base to tip, as in the 

 corn and Iris, and those in which they run from base to the 

 margins, as in the pickerel weed and calla. Leaves may also 

 be divided on a basis of form into (a) simple leaves (Fig. 49) 

 with but one continuous blade and (&) compound leaves, which 

 have two or more blades or leaflets attached to a common 

 petiole. The compound leaves are of two types, the pinnately 



