CLASSIFICATION OF ANGIOSPERMS. 229 



(p. 558) protrude. The grain is somewhat ovate or triangular, 

 flattened, pointed at the base, grooved on one side, indicating the 

 position of the embryo, from 10 to 15 mm. long and about 10 mm. 

 broad, more or less translucent, and varies in color in the different 

 varieties. The constituents of the corn grain are 50 to 75 per cent, 

 of starch; about 10 per cent, of proteins; 4.29 per cent, of a fixed 

 oil; about five per cent, of sugar, and 1.29 per cent, of ash. 



There are a large number of varieties and sub-varieties of Zca 

 Mays, some of the former being ranked as species. The follow- 

 ing well defined varieties may be mentioned : 



(i) Zca Mays ez'crta, to which belong the pop-corns. The 

 size of the ears and grains is about one half or less that of the 

 other corns ; the grains have a more or less translucent and horny 

 endosperm, the cells of the latter containing numerous compactly 

 arranged polygonal starch grains, which are from 7 to 10 /u, in 

 diameter and have a central rarified area from 2 to 7 /x in diam- 

 eter. It is owing to the structure of the starch grains that the 

 peculiar popping of the corn grains results when they are heated. 

 Heating the corn grains at 145 to 160 C. for from 4 to 10 min- 

 utes causes the bursting of the starch grains, and at the same time 

 a rupture of the cells and splitting of the pericarp into 4 parts. 

 The white appearance of the popped grains in due to the inclusion 

 of air in the bursted cells. During the heating the starch is con- 

 verted into a soluble form and this gives popped corn its nutritive 

 value. Some of the flint and dent corns show a similar tendency 

 to pop when heated, but it is only in those parts of the endo- 

 sperm that are horny and the cells of which contain compactly 

 arranged polygonal starch grains in which the rarified area is at 

 least from one-tenth to one-fifth the diameter of the entire grain. 

 Pieces of the pop-corn, as well as the horny portions of some of 

 the flint and dent corns, will pop as readily as the whole grains. 



(2) Zea Mays indentata yields the dent or flint corns, the 

 grains of which have a corneous (horny) endosperm on the sides 

 and are indented at the summit, owing to the shrinking of the 

 cells which contain more cell-sap and less compactly arranged 

 starch grains. 



The starch grains in the cells of the horny endosperm resem- 

 ble those of pop-corn, but the starch grains in the other cells are 



