FIELD CROPS 289 



and potatoes. Sometimes they have swollen leaves, as 

 in the case of onions. The size of these swollen parts has 

 been greatly increased, by cultivation and selection, 

 from that which is found in the wild plants. Thus 

 the "wild turnip/ 7 which is a common weed in our 

 fields, shows little indication of the possible develop- 

 ment into the Swedish turnip or ruta-baga, or into the 

 cabbage. And the wiry root of the wild radish of our 

 fields does not much resemble the tender breakfast 

 radish from which it is derived. Similarly, the large 

 mealy potatoes in our markets do not greatly resemble 

 the little tubers as large as a marble which we see in 

 the wild potato of Chile. * , 



As tubers must grow larger in the soil, it follows that 

 the soil must be kept loose around them, unless it is 

 naturally sandy. Hence they are " hoed " crops, and 

 need cultivation during their growth. We have in the 

 case of beets and turnips varieties which grow mainly 

 above ground, and are therefore less particular in re- 

 gard to soil and cultivation. 



Root crops take a great deal of potash from t^ 

 soils and fertilizers must be adapted to this 



need. They are used very largely for human food as 

 well as for stock, but along with them other foods must 

 be eaten which contain more nitrogen and phosphates. 

 Such foods are grains and legumes, or (for stock) 

 hay. 

 The potato, commonly called Irish potato because 



