FORM AND STRUCTURE 5 



plained, which is carried to so great a degree in certain cereal 

 varieties or in all varieties under favorable conditions. 



In minute structure the culm is characterized by the 

 presence of a large amount of hard tissue (sclerenchyma), 

 which gives it great firmness. This tissue often takes the 

 form of rings lying just beneath the epidermis and is closely 

 associated with fibro vascular bundles (Fig. 2). 



FIG. 2. Part of cross-section of a culm of wheat : E, epidermis ; 

 P, parenchyma ; O, fibrovascular bundle ; K, vessel ; S, sclerenchyma. 



3. Leaves. All cereals have alternate two-ranked 

 leaves. Tufts or bunches of leaves are often formed 

 near the ground. A cereal leaf consists of two parts, the 

 sheath and the blade. The sheath incloses the culm as 

 in a tube, but is split down the side opposite the blade, 

 and its two edges overlap, the" outer edge being raised 

 slightly. There is an appendage extending upward at the 

 line of union of the sheath and blade, called the ligule. 

 The glume of the flowers corresponds to a sheath, the blade 

 being absent or reduced to the form of an awn. Near 

 the ligule there are also two ear-shaped appendages 



