CHAPTER X 

 TRITICUM (Wheat) 



Habit of Plant. — Wheat is an annual. Under our cultural 

 conditions, there are two seasonal forms, winter annual, or 

 winter wheat, and summer annual, or spring wheat. 



Roots. — Wheat has a fibrous root system. In the germina- 

 tion of the grain, the primary root (Fig. 2) takes the lead; 

 very soon, two secondary roots appear on either side of the 

 primary, thus forming a whorl of three. Later, other roots 

 may be added to these. This whorl constitutes the primary 

 or temporary root system. It usually dies before the plant 

 is fully grown. Permanent roots appear in whorls at the 

 nodes some distance above the three temporary roots. The 

 first whorl of permanent roots is generally about i inch below 

 the soil surface, no matter at what depth the grain was 

 planted (Fig. 3) . In their growth, the whorls of permanent 

 roots curve outward and then downward, taking an almost 

 vertical course. They branch very freely near the soil sur- 

 face and form within the first foot a fine network, which 

 constitutes a large absorbing surface. However, many of 

 the roots of wheat reach a depth of 4 feet, or even more under 

 favorable soil conditions. Nobbe observed that the aggre- 

 gate length of all the roots of a one-year-old wheat plant 

 amounts to 500 to 600 meters. The number of roots increases 

 with the number of tillers. 



Stems. — The stems of wheat are of the general grass type. 

 In wheat, there are usually six joints (internodes), the sixth 

 being the spike-bearing one. The lowest joint usually re- 



91 



