STRUCTURE OF WHEAT 33 



varies widely with the variety, soil, climate and culture. In 

 this country a good spike of wheat will usually contain from 

 fifteen to twenty fertile spikelets and contain from thirty to fifty 

 grains. There is a marked difference between the length of 

 the spikes of English and American grown wheats. In the 

 United States the length of the spike varies from three to four 

 and a half inches, a common length being three and three- 

 fourths inches. Hallet has reported raising a spike of wheat 

 eight and three-fourths inches long and containing 123 grains 

 produced by five years of selection and favorable environment 

 ^rom a spike four and three-eighths inches long and containing 

 ^orty-seven grains. Investigations by Lyon seem to show no 

 relation between average weight of grain and the number on 

 the spike. 



The yield of wheat is affected by four factors, viz., (i) the 

 aumber of spikes per a given area, (2) the number of spikelets 

 •n a given spike, (3) the number of grains in a spikelet, and 

 (4) the weight of the grain. While there is no probability that 

 !such results as were reported by Hallet can be obtained in this 

 country, it seems that the most hopeful method of increasing 

 the yield is by increasing the number of spikelets in a spike. 



The spike varies in compactness and in form. When viewed 

 side wise it may be straight or curved ; may taper toward apex, 

 both ways or have uniform sides, or may be clubbed at the 

 upper end. The tip may be acute on account of undeveloped 

 spikelets or blunt because they are well filled. The base of the 

 spike may be tapering or abrupt for similar reasons. When 

 viewed endwise the spike may be square, flattened with spike- 

 lets or flattened across spikelets. 



60. The Grain. — The wheat grain is a unilocular, dry, in- 

 dehiscent fruit called a carj'opsis, with a thin membranous 

 pericarp adnate to the seed, so that pod and seed are incorpo- 

 rated in one body. The grain is longer than broad, hairy at 

 the apex, slightly compressed laterally, has a deep furrow on 



