104 



FIELD CROP PRODUCTION 



wheat and rye are hairy, while in barley and oats they are 

 smooth. The lower leaves wither and die as the plant 

 approaches maturity, and at the beginning of ripening only 

 the upper leaf and the topmost internode are green. 

 87. The spikelets. — A spikelet is composed of two 

 outer glumes, inclosing from two to 

 five flowers, each with a flowering 

 glume and palea. In the wheat plant 

 only one spikelet grows from each joint 

 of the rachis. The rachis may be de- 

 fined as that part of the stem which 

 passes up through the head. The 

 joints of the rachis are close together, 

 thus forming a compact head or spike. 

 The number of spikelets per head 

 varies with different varieties, the 

 thickness of planting, the condition of 

 the soil, and ■ with the weather. The 

 number varies from 10 to as many as 50 

 or more. In fertile soils more spike- 

 lets are produced per head than in poor 

 soils. A thin rate of seeding also favors 

 the production of a larger number of 

 spikelets. Some varieties naturally 

 have a larger number of spikelets per 

 head than do other varieties. At the 

 base of the head there are usually one or more sterile 

 spikelets, — that is, spikelets in which the flowers do not 

 become fertilized and produce kernels. This varies with 

 the growing season and with the rate of planting. Un- 

 favorable grov/ing seasons and a thick rate of seeding are 

 favorable for a large number of sterile spikelets. The 

 spike or head may vary in length and in shape. The 



Fig. .33. — Variation 

 in size of head and 

 number of spikelets. 



