220 TILLEES OF THE GKOUND CHAP. 



have learnt step by step all the great lessons. 

 First, the} 7 found out which plants were best worth 

 cultivating, and this the first and greatest lesson 

 was learnt in three special parts of the earth's 

 surface only. In order that these plants might be 

 useful to all the earth, then, they had to spread 

 out in all directions from the places where they 

 originated, so that West might learn from East, and 

 West again might give back a hundredfold for all 

 that she received. 



As they spread, and were cultivated over larger 

 and larger areas, the food -plants, we saw, were 

 altered and improved, fitted for new countries 

 and new conditions. We saw that at first the 

 process of improvement was slow and almost un- 

 conscious, but gradually as knowledge increased 

 it became quicker and more certain, until now 

 the gardener can mould his plants almost at his 

 will. 



But, as man's skill increased, so also his enemies 

 seemed to multiply. No sooner did the earth 

 begin to bring forth abundantly than the struggle 

 with disease and with destructive insects became 

 fiercer, and the skill which had produced new 

 plants, and made them more productive, had to be 

 turned to the ways of protecting these plants 

 against caterpillar and fungus, against beetle 

 and fly. 



