Wilson — Unsound Mendelian Developments. -411 



which is abseut iu the recessive. The tall pea is tall owing to the presence in 

 it of a factor for tallness, but iu the absence of this factor the pea remains a 

 dwarf. All peas are dwarf, but the tall is a dwarf plustlie factor which turns 

 it into a tall. Instead of the characters of au alternative pair being due to 

 two separate factors, we now regard them as the expression of the only two 

 possible states of a single factor, viz., its presence or its absence." 



Dealing with the general question, Professor Bateson writes that " All 

 observations point to a conclusion of great importance, namely, that a 

 dominant character is tlie condition due to tlie presence of a definite factor, 

 while the corresponding recessive owes its condition to tlie absence of the 

 same factor.'" 



Without doing more tiian remark that tlie latter part of Professor Piinnett's 

 statement virtually makes the presence and absence theory turn two factors 

 into one, only to be obliged immediately to turn the one factor into two again, 

 it may be said that these two statements are ambiguous. They are open to 

 two interpretations, and unfortunately the worse one is frequently taken. If 

 these statements mean that the long factor turns a short pea's progeny tali, 

 and that on its removal the tall pea's progeny become short again, hut that the 

 short pea is still due to the same cause or causes that made it short before the intro- 

 duction of the long factor, there is no ground for quarrel with the statements 

 further than that they do not state the whole case. But this is not the usual 

 interpretation put upon them ; and the other interpretation, which is probably 

 taken because of the above incomplete statement, is that, while a factor 

 itself is the cause of a dominant character", its absence is the cause of the 

 corresponding recessive. This credits a thing which is absent witli the work 

 done by another thing which is present but overlooked. The real state of affairs 

 is that the absence of the long factoii may be the cause of the 



ABSENCE OF THE LONG CHARACTER, BUT ir IS NOT THE CAUSE OF THE PRESENCE 

 OF THE SHOUT. 



If long and short peas were crossed and re-crossed again and again so as 

 to produce alternate generations of long and short peas, the view might be 

 taken that the absence of the long factor allowed the effect of the short to 

 become visible, but that would not deprive the short character of its own 

 essential cause. Under such circumstances the absence of the long factor might 

 be regarded as a "condition" necessary to the emergence of the short 

 character ; but this does not justify us in preferring this condition as the cause 

 of the production of the short character over a still more essential condition. 

 If a pedestal supporting a bust be knocked away, we are not justified in 



1 Mendel's " Principles," p. 54. 



