36 FLOURS. 



(25) Maize Flour. 



The anatomy of the grain of maize is analogous to that of the 

 fruit of other cereal grasses ; it is characterised by the follow- 

 ing particulars : Below the epidermis of the pericarp are two 

 layers of cells that exhibit marked differences, those of the one 

 having pitted and relatively slightly thickened walls, those of the 

 other being smooth and relatively strongly thickened. Within 

 these layers is one of irregular cells with lacuna (transverse cells), 

 and next to this the tubular cells that form the inner epidermis of 

 the pericarp. The tubular cells are smaller, more numerous, and 

 closer together than they are in wheat. During the ripening of the 

 grain the seed-coats disappear almost entirely. 



Maize starch is well characterised by the shape and size of the 

 grains, those from the outer horny part of the endosperm being 

 polyhedral and angular, whilst those from the inner mealy part are 

 rounded. The details given under " Maize Starch " (see before) 

 allow of this flour being easily distinguished from that of other 

 cereals. 



The diagnostic characters of maize flour are : 



(a) The characteristic starch grains. 



(b) The hypsderma. 



(c) The numerous small tubular cells. 



