CHAPTER VI 



THE STEMS : " TILLERING," " SHOOTING," AND " LODGING " 

 GENERAL MORPHOLOGY 



THE culms or straws are erect, elastic, cylindrical, and in some wheats, 

 especially T. dicoccoides, T. turgidum, and T. Polonicum, more or less 

 furrowed, with smooth or scabrid surfaces. The upper parts in a young 

 state are green, and carry on the process of assimilation extensively, the 

 straw and investing leaf-sheaths being able to supply sufficient food to 

 mature and ripen grain even when the leaf-blades are removed at the 

 time of flowering of the ear. 



When ripe the colour in most wheats is a pale yellow ; in some, how- 

 ever, the upper internode is a characteristic purple tint about the time of 

 harvest. 



In normally grown plants of Bread wheat the majority of the culms 

 possess six nodes, although straws with seven and also with five are not 

 infrequent. 



At the nodes, which should not be confused with the swollen bases of 

 the leaf-sheaths, the stem is much contracted in diameter and always solid, 

 the vascular bundles being there crowded together and interlaced to form 

 a strong diaphragm between two internodes (Fig. 39). 



In most varieties of Bread wheats the internodes are hollow, but 

 in many kinds of Rivet and Macaroni wheats the central part of the straw 

 is completely filled with a soft pith. In the hollow straws the cavity 

 begins to form when the young internode is about half an inch long, the 

 separation of the cells appearing first in the upper part of the internode 

 just below the diaphragm. 



The whole length of the lower, and much of the upper internodes are 

 invested by the leaf-sheaths, which function as protective and supporting 

 structures to these sections of the straw, especially when the latter are 

 immature. 



The length attained by a straw is influenced by a number of inde- 

 pendent factors, some races, e.g. Rivet wheats (T. turgidum) and Macaroni 



