CLASSIFICATION OF AMERICAN WHEAT VARIETIES. 23 



The keys and descriptions which are used here to distinguish and 

 identify varieties are based on characters which show considerable 

 variation and therefore are of value. 



MORPHOLOGICAL CHARACTERS. 



The following pages present in detail such morphological char- 

 acters of the wheat plant as have been found in the present study 

 to be of the most taxonomic value. The characters used to distin- 

 guish the different species, subspecies, and lesser groups in the 

 genus Triticum are often of no higher rank than the characters used 

 to distinguish the cultivated varieties. 



In the preparation of the key certain primary characters have 

 been used in a regular sequence. These characters are designated as 

 major characters, and in the key they are printed in capitals. 

 Certain other characters are used in the key to separate further, the 

 closely related varieties. For this purpose any character is used 

 which serves to distinguish the varieties under discussion. The 

 same characters may not be used in two successive cases and they 

 are not used in any definite order. These secondary characters are 

 printed in ordinary type and are designated as minor charac- 

 ters. The general principle followed in the choice of characters in 

 the key was to progress from those most easily observed and most 

 often occurring to those least easily observed or least often occur- 

 ring. The principle governing the sequence of characters in the 

 key is to progress from the absence of the character, as awnlessness, 

 to the presence of the character and from the smaller size to the 

 greater. 



The descriptions of the wheat varieties are arranged in a logical 

 order of plant development. The major and minor characters used 

 in the key are included in their proper places in the descriptions, 

 as are many minor characters not used in the keys. 



All of the taxonomic characters which are used in the keys and 

 descriptions of cultivated varieties are considered below in the order 

 of their appearance in the descriptions. 



PLANT CHARACTERS. 



Certain plant factors which are genetically different in the several 

 varieties are of value for classification purposes. These are the 

 habit of growth, the period of growth, and the height of the plant. 



HABIT OF CiROWTH. 



All wheat varieties are here classified as having winter habit or 

 sprin:.'' babil of growth. These characters are shown in Plate II. 

 In the keys <o the cultivated varieties they occupy the seventh 

 and last major position. Varro (in Columella, 74) writing before 



