STRUCTURE OF WHEAT 35 



62. The Endosperm. — Under the microscope the endosperm 

 is seen to consist of large elongated thin-walled cells, with theii 

 longer axis usually at right angles to the surface of the grain. 

 These cells are filled with starch granules varying in size and 

 form, but when full grown they are rounded or oval in shape 

 and reach a diameter of thirty-seven micromiUimeters, or 675 to 

 the inch.^ The composition of the flour shows the presence of 

 ash and proteids, although under the microscope usually starch 

 only can be seen in the mature grain. M. E. Fleurent has 

 separated the endosperm from the rest of the grain and has 

 subdivided it into three portions from the center outward.^ 

 There was a material variation in the per cent of gluten in the 

 endosperm of different varieties and a marked variation in 

 successive portions from center outwii-rd, both in the per cent of 

 gluten and the proportion of glutenin to gliadin. (70) Proceed- 

 ing from center outward, the per cent of gluten varied in a French 

 variety from 7.37 to 9.51, in an Indian variety from 8.03 to 10.24, 

 and in a Russian variety from 10.88 to 13.22. The per cent of 

 flour was largest (73.02 per cent) in the Indian variety and 

 least (67.25 per cent) in the Russian variety. 



63. The Aleurone Layer. — The endosperm, along with the 

 embryo, is enclosed in a single row of comparatively large cells 

 rather regular and rectangular in transverse or cross section. 

 When viewed perpendicular to the surface these cells are 

 irregular in form. The cells are filled with a substance similar 

 in composition and physical properties to that found in the 

 embr^^o, and are referred to as aleurone or gluten cells. The 

 gluten of wheat flour does not come from the aleurone layer 

 but from the endosperm. 



64. The Bran. — The aleurone layer is enclosed in the 

 nucellus, which in the mature wheat grain is a single layer of 

 collapsed cells or may be wanting. This is enclosed in the 



1 Neb. Bui. 32, p. 109. 



•> Compt. Rend. Acad. Sci., Paris, 126 (1898), No. 22, pp. r^g2-lS95. 



