TRITICUM 



103 



SO the principal protein found in the starchy endosperm, and 

 thould not be used in connection with the aleurone layer. 



Starchy Endosperm. — This is made up of large, somewhat 

 elongated, thin-walled cells. The longer axes of the cells 

 are usually at right angles to the grain surface. They are 

 filled for the most part with starch grains. Protein granules 

 may be seen among the starch grains by appropriate stain- 

 ing. Most, if not all, of the wheat starch and all of the 



jlarchy f 

 endosperm- + — — 



aleurone- 



xuiellum- 

 coleopUle 



epiolajr ^ 



•^ rool 



coleorhiza 



groove 



oiimdnc 

 ebithelmm 



^vascular 



bundle of 



jcutellum 



-^rowin^ 

 W stem 



Fig. 36. — Part of a median lengthwise section of a grain of wheat; much 

 enlarged. (After Strasburger.) 



gluten occur in this part of the endosperm. The percentage 

 of gluten increases from the center outward; those cells 

 next to the aleurone layer contain the largest amount. 

 Embryo. — ^A median lengthwise section of the grain of 

 wheat shows well the structure of the embryo (Fig. 36). 

 The seminal roots point toward the micropylar end. They 

 consist of a primary rootlet with two pairs of laterals. 

 According to Brenchley, a fifth lateral rootlet is foimed in 

 addition to the two pairs usually described. These rootlets 

 are surrounded by the root sheath or coleorhiza. A very short 



