xi CHIEF KINDS OF FOOD-PLANTS 135 



A considerable number of other seed -producing 

 plants are also cultivated, but perhaps we need only 

 mention buckwheat, which is not a true grain, but 

 is used instead of a grain in some places, because it 

 is easily grown, even on poor soil. 



When we come to consider the plants which 

 man cultivates for the sake of their underground 

 parts, we find that no two families stand out as do 

 the Grass family and the Pea family among seed- 

 producing food-plants. There are, however, a great 

 many families which include one or two useful 

 plants. 



If we begin with cool climates like our own, 

 we find that the members of the Cabbage family 

 are often important, either directly or indirectly. 

 Thus, if it was not for the different kinds of 

 turnips and swedes, farmers could not keep their 

 sheep alive during the winter, and we could not get 

 mutton to eat. That is, though perhaps turnips do 

 not matter a great deal to us directly, they matter a 

 great deal indirectly. 



More important to us is the potato, which is 

 the underground stem of a plant of the Deadly 

 Nightshade family. The potato is a plant which 

 likes a cool climate, and requires a great deal less 

 sun than grain does. It is this which makes it so 

 useful a plant in Ireland, where the damp prevents 

 wheat from ripening. It is very interesting to 



