VI 



THE SPKEADING OF FOOD-PLANTS 69 



The result is that when the hardy kinds are 

 grown in Arizona, practically they do not grow at 

 all during the winter, mild though it is, while the 

 Peruvian kind keeps on growing steadily, so that 

 by the end of February, when it is still winter, it 

 has grown to a height of two feet, and is ready 



FIG. 16. A Field of Peruvian Alfalfa. 



to be cut as hay. Thus while the other alfalfas 

 in Arizona have only a short growing period, 

 the Peruvian kind goes on growing continuously, 

 and is therefore always taller, and always gives 

 better crops than the others. For parts of Arizona 

 it is the best kind, but as farther north it is 

 almost always killed in the winter, it is quite 

 unsuitable. 



