CHAPTER V 



THE LEAVES 

 GENERAL MORPHOLOGY 



THE wheat plant possesses several forms of leaves, viz. : (i) the scutellum, 

 (2) the coleoptile, (3) the ordinary green foliage leaves, (4) the prophylls 

 of the lateral axes, and (5) the glumes of the inflorescence. The scutellum 

 has been considered already and the glumes will be dealt with later. 



The coleoptile or plumule sheath which encloses the first shoot is a 

 hollow cylindrical structure with a bluntish apex slightly curved to one 

 side. I regard it as the primary prophyll or a leaf-sheath the blade of 

 which is absent. Near its tip, on the side away from the scutellum, is a 

 small slit through which the foliage leaves emerge (Figs. 9, 35). 



In some forms of wheat the coleoptile is pale green or colourless, 

 in others it is pink. The extent of its development varies with the depth 

 at which wheat-grains are deposited in the ground. In crops drilled 

 about an inch deep in the ordinary way in the field it comes to the surface 

 or a few millimetres above it. In the case of grains sown i -2 cm. (about 

 half an inch) below the surface, the coleoptile grows to a length of 1-5 

 cm. : in those sown 2-5-5 cm - ( I * 2 inches) it usually measures about 

 3-5 cm., while in grains covered with 10 cm. (about 4 inches) of soil it 

 reaches a length of about 6 cm. 



It has few chloroplasts in its tissues and possesses little photo- 

 synthetic power : it functions chiefly as a protective cover to the young 

 foliage leaves during their upward growth through the soil. 



The foliage leaves of wheat, like those of grasses generally, are arranged 

 on the culms alternately, in two opposite vertical rows, each leaf having a 

 divergence of 180 from the next above and below it. This relationship 

 is seen in the position of the coleoptile and first foliage leaf of the embryo. 



In the case of lateral shoots, the first leaf is a binerved prophyll, some- 

 what resembling in form the coleoptile already described. It is semi- 

 cylindrical, with an opening at the apex, through which the green foliage 

 leaves emerge later. The upper part is green with deflexed hairs along 



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