v THE SPEEADING OF FOOD-PLANTS 61 



more and more of the same plants, and for a few 

 years all goes well. Then one year an early frost 

 comes and his crops blacken in the field before 

 they are ripe, with the result that the farmer is 

 half ruined. If he learns in this way that he will 

 be likely to lose his harvest perhaps every five or six 

 years, it is clear that the particular plant is not 

 worth growing. But if the weather had been 

 observed for ten years or so, it would have been 

 possible to tell him that it was an unsuitable crop, 

 and so prevent him ruining himself. Therefore, 

 before the Bureau of Plant Industry in the United 

 States recommends farmers to grow particular crops, 

 it must not only find out what climate the plant 

 requires ; it must also collect facts about the 

 climates of different regions, so that it is able to 

 say this region is suitable, that region is not. 



All this means a great deal of hard work and a 

 great deal of expense, but the people of America 

 have learnt by experience that it is better that 

 the Bureau of Plant Industry should do this 

 work, rather than that individual farmers should 

 have to do it for themselves, and perhaps lose 

 everything in the process. Even with all the 

 experiments it is impossible to avoid serious loss 

 sometimes. For instance, when Alaska began to 

 be opened up, the people tried to grow the same 

 plants that flourished in the Great Plains, where 



