FERNS, FOSSILS AND FUEL 
widely in America came originally from Asia or Europe; 
while the Western Hemisphere, in turn, has made a 
number of plant contributions to the Old World. 
These humanly controlled migrations of food plants, 
of which some of the more important examples are noted 
in this chapter, have constituted an important economic 
factor in the history of civilization. 
The plants that now, under intensive cultivation, sup¬ 
ply the great bulk of the world’s food, are all descendants 
of the primitive flowering plants that first made their 
appearance so inconspicuously in the Jurassic period, 
millions of years ago, when the cycads dominated the 
landscape. 
The ancestors of our modem food plants were scraggly 
things with small, uninviting fruit, which would be of 
little commercial value today. Under cultivation through 
many centuries they have become transformed so that 
they now bear little resemblance to the wild plants from 
which they are descended. 
In recent years, marvelous improvements in all kinds 
of food plants, and even the creation of entirely new 
varieties, have been made possible by scientific selection 
and interbreeding. The work of the late Luther Burbank 
in this field has produced spectacular results. Splendid 
new types of wheat and corn have been produced, which 
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