LEAVES 



155 



In fact, most stipules have a structure and function similar 

 to those of leaves. In smilax the stipules are modified as 

 tendrils; in black locust the stipules are modified as thorns 

 and these thorns are persistent for several years. 



FIG. 92. Forms of Bases. 1, Acute, spicebush (Benzoin cestivale); 2, 

 cuneate, white oak (Quercus alba) ; 3, acute, dogwood (Cornus Florida) ; 4, 

 obtuse, choke-cherry (Prunus virginiana) ; 5, truncate, poplar (Populus 

 tremuloides) ; 6, oblique, slippery elm ( Ulmus fulva) ; 7, cordate, aster (Aster 

 cordifolius) ; 8, reniform, wild ginger (Asarum canadense) ; 9, auriculate, 

 aster (Aster novoe-anglice) ; 10, hastate, pigweed (Chenopodium album) ; 11, 

 hastate, sheep sorrel (Rumex Acetoselld) ; 12, sagittate, tear-thumb (Poly- 

 gonum sagittatum) ; 13, sagittate, arrowhead (Sagittaria latifolia). 



Relation of the Blade of Sessile Leaves to the Stem. The 



attachment of sessile leaves to the stem is normal if the base 

 of the blade is grown fast to the stem, as in Erigeron; it is 

 decurrent if the blade is attached to the stem for a consider- 



