Chapter Nineteen 

 HEREDITY AND VARIATION IN PLANTS 



In the previous chapter we have seen how crossing and 

 selecting may lead to the production of new and improved 

 varieties. We also discussed some of the fundamental 

 reasons for getting such results. The discovery of Mendel's 

 laws and cytological work on the behavioi" of chromosomes 

 has removed plant and animal breeding from the realm of 

 superstition and magic and established it as a science. 



But, we must not forget that plant breeding has been 

 going on in some form or other for thousands of years. For 

 all our new knowledge, we have not added a single new staple 

 food to our diet since the stone age! Wheat, barley, rice, 

 bananas, cocoanuts, dates are all very ancient crops, and are 

 staple crops today. Archaeologists who have studied the 

 upper basin of the Nile (Dorsey, De Rustafjaell and others) 

 believe that barley was grown in Egypt at a time when 

 Northern Europe was still covered with ice (10,000-15,000 

 years ago). While corn and the potato may not be such 

 ancient crops, they were developed by stone age Indians in 

 the Americas. Stone age farmers improved their crops 

 mainly by selection, but the results that they achieved attest 

 their diligence. Stone age men domesticated and improved 

 all our major crops. The American Indians had all the 

 major kinds of corn that we have today. They had pod 

 corn, pop corn, dent corn, flint corn, sweet corn, red, blue, 

 purple, white, and yellow corn. For all our knowledge of the 

 ten pairs of chromosomes, our use of X-rays and our inten- 

 sive breeding, we have contributed much less toward the 

 production of a staple crop than stone age Indians. 



We generally expect the offspring to resemble its parents. 

 In fact, this principle is so pronounced that it has been recog- 



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