92 BOTANY OF CROP PLANTS 



mains short, sometimes less than i millimeter long; the second 

 joint also remains short; the sixth one is the longest. 



Leaf. — The wheat leaf is of the ordinary grass type. The 

 blade varies considerably; the sheath is spUt; the ligule is 

 thin and transparent; the auricles are conspicuous, although 

 not as prominent as those in barley. 



Inflorescence. — Wheat flowers are arranged in spikelets 

 and the spikelets into a ''head" or spike (Fig. 38). The 

 spike varies in size, compactness and form in the different 

 types of wheat. Fifteen to twenty fertile spikelets in a head 

 is a fair average, but spikes have been observed with a 

 number considerably greater. An abundance of water in 

 the soil during the early stages of development has been found 

 to increase the number of spikelets in a head. The racUs 

 or main axis of the spikelet is zigzag in shape (Fig. 48). 

 Each joint of the rachis is flattened and curved, the concave 

 surface being on the side next to the spikelet. There is but 

 one spikelet at each joint of the rachis. There are usually 

 numerous short so-called "basal hairs" at the base of each 

 spikelet. The lower spikelets of the head are often sterile; 

 less frequently, the terminal spikelet is sterile (as in einkorn). 



Spikelet. — The number of flowers in a wheat spikelet 

 varies from two to five. It has been shown that the number 

 of flowers that reach maturity in a spikelet may be increased 

 by an ample supply of water during the period when the 

 flowers are developing. It is quite probable that there is 

 a "critical period" in the life of the plant at which time the 

 supply of moisture coming to the plant has the maximum 

 effect in the production of flowers. This critical period is 

 probably during the early stages of flower formation, quite 

 a while before the time of heading. 



The wheat spikelet dissected in Fig. 29 has four flowers, 

 three of which have matured grain. The fourth flower is 



