CLASSIFICATION OF ANGIOSPERMS. 229 



culms, which are grooved on alternate sides in the successive 

 internodes and from the nodes of which arise aerial secondary 

 roots. The leaves are alternate and consist of three parts: (a) 

 a blade, which is long, broadly-hnear and tapering toward the 

 apex, the tip being pendulous ; (b) a lower sheathing portion 

 which is open; and (c) a short, translucent, somewhat hairy 

 ligule, situated between the sheath and the blade. The flowers 

 are monoecious, the staminate, which are arranged in a terminal 

 panicle, maturing first; the pistillate occur in axillary spikes, the 

 axes of which constitute the corn cob. They are enclosed in 

 spathe-like bracts or husks, from which the long filiform styles 

 (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 diflferent 

 varieties. The constituents of the corn grain are 50 to 70 per cent. 

 of starch ; about 10 per cent, of proteids; 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 Zea 

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

 ing well defined varieties may be mentioned : 



(i) Zea Mays everta, 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 /t 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 is 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 



