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THE AMEBIC AX NATURALIST [Vol. XLIX 



in their gametes. Corn and cotton, species usually cross- 

 pollinated, have 10-12 and 20-28 chromosomes, respect- 

 ively, in their germ cells. These species all have been 

 under cultivation since before there has been recorded his- 

 tory. Many varieties of each exist. It is not at all im- 

 probable that with thousands of years of cultivation and 

 selection under diverse conditions, mutations in most of 

 their chromosomes have persisted. If, then, improvement 

 means working on character complexes that involve al- 

 most all of the plant functions, it does not seem improb- 

 able that the actual difference in the difficulty of improving 

 wheat and tobacco is as 4 s :4 24 , or about 1 to 4,295,000,000. 

 In like manner corn and cotton compare in the ratio 

 4 10 : 4 28 , or 1 to 68,720.000,000. And is it not true that 

 modern improvement in most of these crops does involve 

 nearly all the plant functions? Yield in wheat involves 

 number and size of grain, and number of culms, with all 

 that these things include in plant economy; yield of to- 

 bacco involves number, size and thickness of the leaves. 

 Quality, a mystical word, is perhaps still more complex. 

 In wheat, it takes in habit of growth of both root and stem 

 and such other characters as go to make up strength and 

 hardiness, thickness of pericarp, size of aleurone cells, and 

 the physical and the chemical character of both endo- 



to each other. In tobacco, it includes thickness and 

 strength of leaf, color, texture and all chemical and physi- 

 cal characters that make for flavor and "burn." 



One may say that this is all very well as a theory, but 

 that it is all theory, and ask what support is given to it by 

 practise. I have had personal experience with but two 

 of these four crops. I have worked extensively and in- 

 tensively with corn and tobacco for some ten years. But 

 I have followed carefully the published experiments in 

 breeding wheat and cotton and have seen several of the 

 more important experiments. And I may say that it ivas 

 my observation of the extreme, difficulty in the experi- 

 ments with cotton and tobacco as compared with com and 

 wheat that led to this theory of the cause. 



