EFFORTS TO INCREASE FOOD RESOURCES 



better to their liking, and some have stayed at home 

 for a while and immigrated later. The barberry can not be 

 planted where wheat is grown because it is a propagator of 

 a rust disease that places an annual tax of an enormous sum. 

 Currant and gooseberry bushes have the same relation to a 

 disease of pine trees and are ruthlessly dug out where the 

 pine trees are first in importance. 



Although loss can be prevented by proper cultural prac- 

 tices and timely applications of chemicals, how much less 

 expensive and how much more satisfactory it is to have 

 plants and animals that are immune to disease and insect 

 injury. The most notable cases of this kind are the rust- 

 resistant wheats and the mosaic-free sugar cane. Certain 

 kinds of tobacco will grow vigorously in soils where other 

 varieties are stunted by root-rot. Cabbages have been 

 developed that will produce an abundant crop alongside 

 fields carrying varieties that are a complete failure. Cow- 

 peas that harbor nematodes in their roots can make no 

 satisfactory growth, but some plants are so constituted 

 that these parasitic worms can not enter them. American 

 grapes, through many centuries of association with root 

 lice, have become immune to injury from their action. Not 

 so the European grapes, that had never known this 

 pest until the early explorers brought back vines from 

 America. Little did they realize what a frightful menace 

 they were bringing to the Old World vineyards. Only by 

 bringing over American vines to use as root stocks and by 

 developing methods of spraying, have Europeans been able 

 to continue grape culture. On their new roots the vines 

 yield more than ever before. 



Few people realize how fast the vegetables, fruits, and 

 flowers are changing. The wheat that goes to the modern 

 steel mill in railroad car, canal barge, and ocean ship is not 

 from the same varieties that the ox cart and saddle pack 

 carried to the stone gristmill a few generations back. The 



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