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THE AMEBIC AX NATURALIST [Vol. XLTII 



as present in the yellow pea and absent in the green pea. 

 "What is to hinder us from describing the green as present 

 in the green pea and absent in the yellow one ! Similarly 

 in the contrast between tall and dwarf, one could perhaps 

 say "presence and absence of dwarf ness on a tall basis" 

 as appropriately as "presence and absence of tallness 

 on a dwarf basis," and there seems no sufficient reason 

 why the palm type of leaf in Primula should not just as 

 well be considered a shortened fern type, as the fern an 

 elongated palm type, or that the thrum is a shortened 

 pin-eye quite as well as that the pin-eye is an elongated 

 thrum. But notwithstanding such difficulties as these, 

 there can be no question that most of the phenomena of 

 Mendelian inheritance are more simply stated in terms 

 of presence and absence than in any other way. 



It has appeared to several writers as a difficulty for this 

 hypothesis that in a number of cases what appears to be 

 the absence of a character is dominant over its presence. 

 There are a number of noteworthy cases of this kind. 

 Thus, in cattle the hornless condition is dominant over 

 horns; in most breeds of poultry white plumage domi- 

 nates over colors and white legs over yellow legs; in 

 snails unbanded shells dominate over banded, and less 

 banded over more banded ; in wheat, smooth heads domi- 

 nate over bearded; in flowers having a yellow plastid 

 color, white is dominant over yellow; in canary birds the 

 presence of a mottled pattern is dominated by its ab- 

 sence, though in most cases color patterns are dominant 

 over their absence. Thus in the mottled varieties of 

 beans, for instance, the mottling factor is dominant over 

 its absence, and in rabbits, the English-marked, Dutch- 

 marked, tan-marked, tortoise-yellow, and agouti patterns 

 are in each case dominant over their absence. 



At several places Hurst states (loc. cit.) that the as- 

 sumption that a certain character is the presence-char- 

 acter would "imply the dominance of that character, " 

 though in eight instances among the 44 he cites, he 

 definitely places the absence dominant over presence. In 



