43 FLOURS. 



(27) Bean Flour. 



The haricot bean, Pliaseolus vulgaris, Linn., possesses an anatomi- 

 cal structure resembling that of other leguminous seeds. In the 

 seed-coat the following layers can be distinguished : (1) An epi- 

 dermis consisting of prismatic cells, radially arranged, like palisade 

 cells ; the walls of these cells are much thickened and possess slit- 

 like pits. (2) A layer of nearly square, or rectangular cells, each 

 containing a large prismatic crystal of calcium oxalate. These cells 

 are often called "bearer cells," and are found in all varieties of 

 beans, but in many other leguminous seeds they are contracted 

 in the middle (in transverse section), and free from calcium 

 oxalate. (3) A layer of parenchymatous tissue. 



The cells of the cotyledons are polygonal and exhibit at their 

 angles either a collenchymatous thickening or more or less con- 

 spicuous intercellular spaces. 



The starch of the haricot bean is in ovoid grains, seldom rounded, 

 sometimes reniform, or exhibiting one or more protuberances. 

 The hilum, which is usually very distinct, is elongated or 

 fissured. In size the large grains vary from 30 to 75/t ; many 

 smaller ones are, however, to be found. The concentric striae are 

 usually distinct. 



Bean flour is often made from the decorticated beans, but, in 

 spite of that, a few fragments of the seed-coat can generally be 

 found. 



The diagnostic characters of the flour of the haricot bean are : 



(a) The remarkable palisade cells. 



(b) The bearer cells with crystals of calcium oxalate. 



(c) The cells of tlie cotyledons. 



(d) The characteristic starch. 



