DIVERSITY OF LEAF-FORMS IN PISTACIA 



Figure 19. Leaves of the pistachio tree (Pistacliia vera) at Sacaton, Arizona, 

 October, 1922, all from the same tree as Figure 20, the, three large leaves from 

 the same twig. The typical leaf-form is shown at the lower right-hand corner, 

 a leaf with two pairs of lateral pinnae which are narrowe.d abruptly to the point 

 of attachment while the terminal pinna has a gradually narrowed or decurrent 

 base. Leaves with only one pair of lateral pinnae ofte^n show a more abrupt 

 narrowing of the base of the terminal pinna which in such cases probably indi- 

 cates a complete fusion of the upper pair of lateral pinnae, with the terminal 

 pinna. Dififerent stages of partial fusion are shown, as in Figure 20. Natural size. 



