LEAF FORMS OF THE OAK WALNUT 



Figure 14. Showing replacement of pinnae by small stipule-like organs, which 

 occurs frequently in leaves of the oak walnut. In some cases both pairs of ipinnae 

 are replaced, either by simple stipules, or by slender, stipule-like organs that serve as 

 pedicels for very small pinnae which are quite variable in form, oval, circular, or 

 cup-like. The cup-like pinnae, or "ascidia," apparently are formed by union of the 

 basal margins below the point of attachment of the leafy portion of the pinna with 

 the stalk. Formation of these cup-like pinnae may indicate a backward growth of 

 the leaf-web, from the apex toward the base along the midvein. Note that in several 

 of these leaves one or both of the lateral pinnae have united more or less completely 

 with the terminal ipinna as in the lower right-hand leaf. Also compare this leaf with 

 Figure 9 to observe the close approximation with the bud-scale leaves of hickory. 



