5i8 THE STRUCTURE OF ECONOMIC PLANTS 



"In its early growth, it is almost entirely confined to 8 inches of 

 surface soil. After extending horizontally to a distance of i to i feet 

 or more, the roots turn more or less abruptly downward and penetrate 

 the second and third foot of soil. Roots may also occur in the fourth 

 foot. Branching is very profuse throughout the root extent, and at 

 maturity, laterals occur to the root tips. Usually the branches are 

 relatively short but so numerous and well rebranched that the absorbing 

 system is very efficient. There is some evidence which indicates that 

 late-maturing varieties root deeper than early ones." 



po 



Fig. 174. A, median longisection of mature flower ; B, berry ; C, floral diagram : an, 

 anther; c/«, corolla; c/at, calyx; or^, ovules; po, terminal pore of anther. (After Robbins, 

 Botany of Crop Plants, P. Blakiston's Son and Co.) 



The Inflorescence and Flower. — The inflorescence is cymose 

 and terminal although it appears to be lateral owing to the sym- 

 podial development of the axis. The five-merous flowers are 

 white, yellow, purple, or blue and are borne on bractless pedicels. 

 The calyx is tubular and lobed as is the gamopetalous corolla; 

 and, at anthesis, the latter may be i to i3'2 inches in diameter. 

 The stamens are alternate with lobes of the corolla and adnate to 

 its tube. They are straight or slightly curved with large, erect, 

 fleshy, yellow anthers that are longer than the filaments. Dehis- 

 cence of the anther is by means of two terminal pores. (Fig. 

 X74, A, C) The pistil consists of two undiverged carpels which 



