TRITICUM 145 



prophylls of the lateral branches; (3) the foliage leaves; and 

 (4) the glumes of the inflorescence. The seedling leaves are de- 

 scribed in connection v^ith the structure of the embryo and the 

 germination of the seedling. 



The first leaf or prophyll of a lateral shoot is binerved, resembling 

 the coleoptile in its conical form and in the apical opening through 

 which the succeeding foliage leaves emerge. It attains a length of 

 an inch or more, and its upper portion is green w^ith deflexed hairs 

 along the tw^o veins. The prophyll is oriented so that its concave 

 or flattened surface opposes the axis from which the shoot enclosed 

 by it arises; but the next leaf is diverged at a 90° angle from the 

 prophyll, and each succeeding one has a divergence of 180°, so that 

 the plane of phyllotaxy is at right angles to that of the axis from 

 which the shoot is diverged. 



The foliage leaf consists of the sheath, blade, and ligule. The 

 sheath encloses the culm, being entire near its base; but its upper 

 part is open on the side distal to the blade, and the outer of the two 

 overlapping edges is slightly raised. The lamina is variable in 

 shape, being narrowly linear to linear-lanceolate, and frequently 

 twisted, the torsion being to the right. The venation is parallel, 

 and the bundles are reinforced by mechanical tissue which gives 

 support to the blade, while further stiffening may result from the 

 presence of silica in the epidermis. The curling or expanding of the 

 blade along its longitudinal axis is controlled by the presence of 

 bulliform or motor cells on the adaxial surface. Stomata occur on 

 both surfaces, but with greater frequency on the adaxial one in a 

 ratio of approximately 10 to 7. The claw-like auricles which 

 develop at the base of the blade, where they loosely clasp the sheath 

 and the stem, are somewhat larger than those of rye and not as 

 prominent as those of barley. In young wheat plants, they are 

 frequently somewhat pubescent; and at maturity the tips and 

 margins may have a few unicellular hairs. The ligule, which 

 arises at the junction of the blade and the sheath and surrounds the 

 stem, is a thin, colorless, membranous structure with an irregular 

 edge that is fringed with small hairs. 



The Inflorescence. — The inflorescence is a compound spike 

 which is usually 3 to 4 inches in length, but may vary from x to 

 5 inches. (Fig. 60.) It may differ greatly in its shape and degree 

 of compactness, the density of the spike being determined in part 

 by the length of the internodes and the distribution of the spikelets. 



