CLASSIFICATION OF AMERICAN WHEAT VARIETIES. 31 



Varieties classed as having clavate spikes are clubbed, that is, dis- 

 tinctly larger and more dense at the apex. This is due to a shorten- 

 ing of the rachis internodes in that part of the spike, which results 

 in a change from dorsoventral to lateral flattening and a broadening 

 of the upper portion of the spike. 



Elliptical spikes are short and quite uniformly rounded at both 

 the base and apex, but are flattened on the sides. Most varieties of 

 club wheat have spikes of this shape. 



In the descriptions of varieties these designations of spike shapes 

 have sometimes been modified to take into account the length and 

 width of the spikes and the overlapping of shapes which occurs in 

 some varieties. 



Spikes that are unusually long are described as linear-fusiform, 

 linear-clavate, etc. If spikes are unusually short that fact is in- 

 cluded in the description. Broad spikes may be described as broadly 

 fusiform or broadly oblong and narrow spikes as narrowly fusi- 

 form, etc. 



Varieties that are nearly intermediate between any of the shapes 

 are sometimes described as oblong-fusiform or oblong to subclavate. 

 By the use of these compound descriptive terms spike shapes are 

 more accurately presented in the description than they can be in the 

 keys, where brevity is imperative. 



DENSITY OF THE SPIKE. 



The differences in shape of spikes shown above are due in part to 

 differences in density. All spikes are described as of three density 

 classes, viz, lax, middense, and dense. These differences are shown 

 in Plate VI. These are minor differences which are used to advan- 

 tage in distinguishing varieties. Seringe (17 h) separated the com- 

 mon wheats into two groups, having lax and dense spikes, respec- 

 tively. Koernicke and Werner (133) described the spikes of many 

 varieties according to different degrees of density. Neergaard (1^7) 

 suggested a formula for use in measuring the density of the spike. 

 Eriksson (88) subdivided the botanical groups of Koernicke and 

 Werner on the basis of density into subvarieties called laxum, den- 

 sum, and capitatum. He measured the density of spikes by de- 

 termining the number of spikelets in 100 mm. of rachis length. 

 Heuze (112) used the spike density along with spike shape as the 

 leading character in separating varieties. Boshnakian (4-8) de- 

 scribed means of measuring density and suggested the name Triticum 

 compacto-capitatum for varieties of club wheat having clavate heads. 



Many measurements have been made by the writers to determine 

 the difference in density of the spikes of the varieties here described. 

 The most definite were found comparable at one station for one year, 

 but otherwise were of little value. It was found necessary to estab- 



