82 



THE WHEAT PLANT 





which ears can be detected, and also of full-grown culms or ear-bearing 

 straws, it is seen that no buds are formed in the axils of five to seven 

 leaves immediately below the ear itself. 



In the ordinary course of events, where wheat is sown at any date 

 between October and the early part of March, 

 the young culms with their ears begin to ex- 

 pand in April. In all the shoots of the " til- 

 lered " plant in which the six leaf-blades of the 

 several culms are visible, both the straw and 

 ear can be readily recognised within the leaf- 

 sheaths, although their combined length is then 

 only about a quarter of 

 an inch (Fig. 68) . Growth 

 advances from this stage 

 onwards with increasing 

 rapidity until the straw is 

 2 or 3 feet high, and the 

 ear, almost full grown, is 

 pushed out of the upper- 

 most leaf-sheath into the 



FIG. 68. Longitudinal sec- 

 tion of a young plant at open air, usually at the 

 the end of 'April. , Rhi- en( j of 



n 



zome ; i, 2, 3, ears. 



June. 



The crop in which the elongation of the culms 

 is taking place is said to be " shooting," the process 

 consisting essentially in the expansion of the stems, 

 which have originated in the previous " tillering " 

 period. 



While growth in length in the young stem is 

 effected by the activity of an apical meristem, the 

 straw also possesses intercalary growing-points, one 

 at the base of each internode, which continue to 

 lengthen the several sections of the culm after the 

 upper part of each has ceased to grow ; these 

 delicate growing regions are protected by the 

 surrounding leaf-sheaths. 



The expansion of the straw proceeds from below 

 upwards, the lowest internode being the first to 

 lengthen (Fig. 69), the growth of this being fol- 

 lowed more or less regularly by the succeeding internodes in numerical 

 order to the sixth or uppermost ; growth also ceases in the same order, 

 the lower internodes reaching their full stature some time before the 

 upper ones have arrived at their maximum length. 



FIG. 69. Longitudinal 

 section through a you ng 

 straw. Lengthening of 

 the internodes just be- 

 ginning ( x 5). 



