26 



33. Use of the food stored in fleshy roots. The parsnip, 

 beet, carrot, and turnip are biennial plants ; that is, they do 

 not produce seed until the second summer or fall after they are 

 planted. 



The first season's work consists mainly in producing the food 

 which is stored in the roots. To such storage is due their char- 

 acteristic fleshy appearance. If the root is planted in the fol- 

 lowing spring, it feeds the rapidly growing stem which proceeds 

 from the bud at its summit, and an abun- 

 dant crop of flowers and seed soon follows; 

 while the root, if examined in late summer, 

 will be found to be withered, with its store 

 of reserve material quite exhausted. 



The roots of the rhubarb (Fig. 22), the 

 sweet potato, and of a multitude of other 

 perennials, or plants which live for many 

 years, contain much stored plant food. 

 Many such plants die to the ground at the 

 beginning of winter, and in spring make a 

 rapid growth from the materials laid up in 

 the roots. 



34. Extent of the root system. The total 



FIG. 22. Fleshy roots 

 of garden rhubarb, length of the roots of ordinary plants is 



About one fifteenth much greater than is usually supposed, 

 natural size They are SQ closely pac k e( i i n the earth that 



only a few of the roots are seen at a time during the process of 

 transplanting, and when a plant is pulled or dug up in the 

 ordinary way a large part of the whole mass of roots is broken 

 off and left behind. A few. plants have been carefully studied 

 to ascertain the total weight and length of the roots. Those of 

 winter wheat have been found to extend to a depth of seven 

 feet. By weighing the whole root system of a plant, and then 

 weighing a known length of a root of average diameter, the 

 total length of the roots may be estimated. In this way the 

 roots of an oat plant have been calculated to measure about 



