III. 



WHEAT. 



I. STRUCTURE. 



51. Relationships. — Wheat belongs to the family of true 

 grasses {Gramineae). The G7'aniineae are characterized by 

 having hollow stems with closed joints, alternate leaves with 

 their sheaths split open on the side opposite the blade. Wheat 

 is included under the tribe Hordeae, in which the spikelets are 

 one to many-flowered, sessile and alternate, thus forming a 

 spike. (59) To this tribe belong also rye and barley, as well 

 as the cultivated rye grasses {Lokwrn peremie L. and Z. itali- 

 cum Beauv.). This tribe also includes some troublesome weeds. 

 Couch grass (Agropyron repens Beauv.), a perennial, was 

 formerly included in the same genus as wheat. Because of its 

 underground stems, or rhizomes, couch grass is difficult to eradi- 

 cate and thus becomes a very 

 troublesome weed in cultivated 

 fields. Darnel {Lolium temu- 

 lentuin L.) is common in wheat 

 fields in Europe and on the 

 Pacific coast in this country, A 

 related species {L. 7'emotuni) 

 occurs in flax fields. 



52 . Roots. — When a grain of 

 wheat germinates, it throws out a 

 whorl of three seminal or temporary roots. The coronal or 

 permanent roots are thrown out in whorls from the nodes. 

 The distance between the temporary roots and the first whorl of 

 permanent roots will depend somewhat upon the nature of the 

 soil, but principally upon the depth of planting. The depth at 

 which the first whorl of permanent roots occurs will vary with the 



Cross section of a grain of wheat through 

 embryo showing tips of three rootlets 

 before germination. (From microphoto- 

 graph by Rowlee.) 



