BETA VULGARIS 



2-47 



depths of 5 to 6 feet. Beginning just below the soil surface and extend- 

 ing to a depth of 6 to lo inches, laterals occur in two opposite rows 

 on the sides of the roots. These begin to appear when the plants 

 are 6 to 8 weeks old and finally occur in great numbers, 6o to 70 per 

 linear inch. Running horizontally 6 to 18 inches or more on all sides 

 of the plant and branching profusely, they form an excellent absorbing 

 system in the surface foot of soil. Numerous larger and longer branches 

 arise usually at depths of 8 inches to 4 feet. They spread from 6 inches 

 to i feet laterally and penetrate deeply into the subsoil. . . . This root 

 habit, however, is greatly modified by variations in soil conditions. 

 In dry soil, the taproot is smaller, pursues a more tortuous course, 

 does not penetrate so deeply, and is branched more nearly to the tip. 

 The larger, deeper seated branches turn downward rather abruptly, 

 reaching depths of 3 to 4 feet. Branching is more profuse throughout. 

 Development of the surface absorbing system may be greatly delayed, 

 although it branches more profusely and may extend even more widely 

 when the soil becomes moist." (Fig. 117.) 



Fig. 117. Diagrams showing habit and extent of root system of the sugar beet grown (^) 

 in dry land ; and (B) in fully irrigated soil. (After Weaver, Root Development of Field Crops, 

 McGraw-Hill Book Co.) 



The two rows of laterals, referred to by Weaver, are usually 

 double rows and the grooves from which they arise are oriented 

 in the same vertical plane as the primary xylem strand of the root. 

 The furrowing and transectional plan of the fleshy axis can be 

 correlated with the mode of secondary thickening of the axis, and 



