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THE AMERICAN NATURALIST [Vol. XL V 



early one as compared with sweet corn in general, to be 

 able to survive at all in Maine. During the fifteen to 

 twenty-live years the ancestors of the Type I corn were 

 grown in Maine it must have been 26 subjected to an oc- 

 casional natural selection, for seed could be taken by the 

 farmers from only plants which had ripened their ears. 

 The somatic organization of some plants is such that 

 they require only a few hours for their life cycle, but so 

 long as sweet corn has the general characteristics of 

 root, shoot and leaf that identify it as Zea Mays it seems 

 reasonable to suppose that there is some limit to the re- 

 duction of the time required for germination, growth 

 and fruiting — an irreducible minimum beyond which 

 selection can not carry it. Surely the fact that Pearl 

 and Surface could not continually reduce the time re- 

 quired for growth while at the same time maintaining 

 a selection for yield of ears and stover may indicate 

 that the irreducible minimum for earliness has been 

 reached in a variety of the physical type they wish to 

 breed. Speaking for myself alone, I must say that the 

 data before us prove nothing against the theory of cumu- 

 lative effect of selection, and they certainly do not fur- 

 nish any critical evidence for the Johannsenian theory. 



It seems to me that Pearl and Surface again tacitly 

 make this unjustifiable assumption that the modification 

 attainable for any single character is practically un- 

 limited when they consider that their failure to increase 

 egg production by selection is a legitimate argument 

 against the potency of selection. Indeed they say of "200 

 egg hens," which lay an egg fifty-five per cent, of the 

 days of the year, "This figure is of some interest as indi- 

 cating what a relatively small proportion of the theo- 

 retically maximum character is being selected to, when 



But why, pray, is two hundred and sixty-five and a 

 quarter eggs per year the theoretical maximum? One 



