210 Plant Biology 



which are connected with the vascular bundles of the stem. The broad 

 portion of a leaf is called the blade. The tissues of the corn leaf are as 

 follows: (1) An epidermis on the upper and lower surfaces composed 

 of one layer of cells. Openings on the surfaces are known as stomata 

 (stom'ata) (Gr. stoma, opening) and are for the exchange of gases. 

 Each stoma is bordered by guard cells to regulate the size of the open- 

 ing. Just beneath each stoma is an irregularly shaped, intercellular (suh- 

 stomal) space for the storage of gases. (2) A mass of compactly arranged 

 cells which contain chloroplasts for photosynthesis. (3) Veins which are 

 vascular bundles composed of phloem and xylem. The true root system 

 of corn is fibrous and quite extensive in order to anchor the plant and 

 to absorb water and nutrients from the soil. Small root hairs are exten- 

 sions of the epidermal cells of certain regions of the roots and serve to 

 increase the absorption area of the root system. A nucleus is usually 

 present near the tip of the hair, and there is a large vacuole. 



The flowers of the corn plant are incomplete and on different parts 

 of the same plant. The tassel at the tip of the stem consists of pollen- 

 bearing stamens (male flowers). Each stamen consists of a stalklike 

 filament at the tip of which is the enlarged, pollen-producing anther 

 (Fig. 58). 



The female flowers (pistils) consist of a series of enlarged ovaries 

 (''kernels") arranged on the corn cob to form the corn "ear." A long 

 style (the "silk" of corn) is attached to each ovary, and the tip of the 

 style, called the stigma, is sticky to receive the wind-desseminated pollen. 

 A pollen tube, for the conduction of pollen, grows through the style to 

 the ovary. Fertilization takes place within the ovary (Fig. 58). 



A grain of corn is really a fruit because it consists of a ripened ovary 

 (Fig. 59). A mature grain of corn consists of an outer pericarp (per" i- 

 karp) (Gr. peri, around; karpos, fruit) firmly fused to the seed coat be- 

 neath. On the concave side of the grain, beneath the pericarp, is the 

 embryo embedded in the extensive endosperm (food). The endosperm 

 is composed of three parts : ( 1 ) a single layer of cells next to the nucel- 

 lus is called the aleurone layer; these cells are filled with grains of pro- 

 tein known as aleurone (alu' ron) (Gr. aleuron, flour); (2) an inner, 

 starchy endosperm; (3) an outer, horny endosperm containing proteins. 



The embryo (Fig. 59) consists of (1) one broad cotyledon for absorp- 

 tion of food from the endosperm, (2) a well-developed plumule consist- 

 ing of a stem and one or more foliage leaves, (3) a very short hypocotyl 

 (hi po -kot' il) {Gr. hypo, under or below; kotyle, cup), (4) a radicle 

 (rad' i kel) (L. radix, root) which is the lower part of the hypocotyl and 



