INTRODUCTION 27 



dages. The gynoeceum may be of the same origin 

 as the stamens,* and carpels may develop into leaf-like 

 structures, but are not so- obviously foliar in origin, 

 being axial or modifications of the main axis. Stamens 

 are not developed at the nodes except hypogynous 

 stamens, the carpels being also usually terminal. 



A leaf consists of a blade or lamina and a stalk or 

 petiole with a sheath below which may bear stipules 

 or not. The sheath may encircle the stem. There 

 may be no leafstalk. The blade varies in venation. 

 Venation, which is usually reticulate in Dicotyledons, 

 is parallel in Monocotyledons. The veins in the 

 former may branch in a pinnate or palmate manner. 



The leaf outline varies considerably and the leaf 

 may be linear, lance-shaped, ovate, elliptical, kidney- 

 shaped or heart-shaped, arrow-shaped, spoon-shaped, 

 hastatC;, etc. The margin may be entire, toothed, 

 scalloped, lobed, dissected. The leaves may be 

 united below or clasp the stem or be narrow below. 

 The leaf is simple when the lobes do not reach the 

 midrib, compound if they do. 



The surface of the leaf may be smooth or hairy. 

 The tip may be acute, with a long point, or blunt, 

 notched, sharply and bluntly pointed. Leaf structures 

 not regarded as true foliage leaves and serving 

 separate functions are cotyledons or seed-leaves, 

 scales, bracts (glumes in Grasses, the spathe in Arum), 

 bracteoles, floral leaves, leaf spines, leaf tendrils. 



The arrangement of the leaves may be in a whorl 



* Which are, perhaps, modified leaf-like structures 



