THE WHEAT PLANT 



meet in a backward pointing V-shaped curve, one or two very fine strands 

 of tracheids anastomosing with them just below their point of union. 



In T. dicoccoides and Indian and Abyssinian forms of T. dicoccum three 

 to six vascular bundles are present in the coleoptile (Fig. 16), a fact which 

 supports the view that the latter is homologous with the leaf-sheath or 

 prophyll rather than with the ligule. The bundles consist of a few small 

 scattered xylem elements of nearly uniform diameter and a mass of phloem 

 protected on the outside by a single or double layer of thick-walled 

 cells (Fig. 44). 



The epidermis of the prophylls is composed of elongated rectangular 

 cells with thin straight walls. Along the two margins of the flat side of 

 the prophyll are reflexed unicellular hairs, and 

 near the apex two lines of stomata run on op- 

 posite sides of the nerves. The mesophyll con- 

 sists chiefly of delicate parenchyma ; the cells of 



FIG. 45. Outline 



FIG. 43. Stoma of the and transverse 



coleoptile (cf. Fig. 49) FIG. 44. Transverse section of a vascular section of a 

 ( x 380). bundle of the coleoptile ( x 280). prophyll. 



the apical portion round the nerves contain chloroplasts, the rest of the 

 tissue being colourless. The convex part of the prophyll is transversed 

 by 10-12 very thin, straight, vascular strands, two stronger bundles 

 running from the base to near the apex in the angles where the convex 

 and flat side meet (Fig. 45). Here and there, especially near the tip, are 

 fine anastomosing lines of tracheids. A well-defined strand of stereome 

 strengthens each of the two angles, and, in addition, two or three cells 

 of rudimentary sclerenchyma are found beneath the outer epidermis of 

 the convex side associated with the fine vascular strands. 



