14 BOTANY OF CROP PLANTS 



as the beet, radish, turnip, parsnip and carrot. In the germi- 

 nation of the beet seed, for example, the primary root pushes 

 out, takes a straight downward course, and gives off a few 

 lateral roots. Hence, the primary root system of the beet 

 consists of one main root extending downward, with a few 

 fine laterals. Adventitious roots do not arise, as in wheat, 

 nor does the primary root system die, as it does in wheat, 

 but the main tap root of the young plant continues to elongate, 

 and to give off lateral roots and rootlets (Fig. 4). The 

 "beet" itself is for the most part an enlarged tap root. The 

 tap root of the sugar beet may reach a depth of 4 feet, and 

 often 6 or 7 feet. The upper laterals are the largest of the 

 branch roots and extend farthest in the soil, spreading almost 

 horizontally 2 to 3 feet. The lower laterals are more vertical 

 and those near the very tip are almost parallel with the tap 

 root. A root system such as possessed by the beet, radish, 

 turnip, parsnip, carrot, dandeHon, red clover, and many 

 other plants is called a tap-root system. 



The Work of Roots. — ^A root system absorbs, anchors, and 

 serves as storage organ. The small, young, tender roots, with 

 their root hairs, are largely absorption roots, but as the plant 

 gets older, new absorptive roots are continually being formed, 

 while the older ones become thick and woody and serve mainly 

 as anchorage organs. Familiar storage roots are those of 

 the beet, carrot, turnip, parsnip, sweet potato, and dande- 

 Hon. The food material stored up by such plants for their 

 own use furnishes a large proportion of the food supply of 

 man. Irish potatoes (tubers) are not roots, but stems, and 

 hence their discussion will be reserved for the proper section 

 in the book. 



Effect of Environment upon Character of Root System. — 

 It is noted, when roots make a vigorous growth, as they will 

 under favorable soil conditions, that there is a very extensive 



