Wilson — Unsound Mendelian Developvients. 409 



that for rose in one case and that for pea in the other. This paragraph is 

 thus inconsistent with the first, and, if it be correct, the descriptions in the 

 next paragraph of rose as " i? no P " and pea as " P no ii! " are incomplete, 

 since they leave out the thing modified by B and P. 



One or other of these two statements, viz., that rose is due to a single 

 factor in the first paragraph, or that it is due to more iu the fourth, must 

 be wrong. 



Consider whether the facts of the case agree with the view that rose and 

 pea combs are each due to single factors. Let RR be the constitution of rose 

 and PP of pea. If RB and PP can be brought in simultaneously to the 

 same comb, they will be brought iu either as non-alternative or as alternative 

 factors. In the former case they may have effects that are independent of 

 each other or they may have effects that cannot be separated by the eye the 

 one from the other, but it is difficult to imagine anything being produced in 

 the second crosses but roses and peas and combs the same as the first crosses. 

 On the other hand, if RR and PP are alternatives, their first crosses will be 

 hybrids of the constitution BP, and their seeon(3 crosses should be of the 

 constitutions BB, BP, and PP in the ratio 1:2:1. But neither of these 

 results is found in the second crosses from rose and pea. The results do not 

 fit the assumption of hybridization, and, on both assumptions — liybridization 

 and combination — there is a comb produced which has no business to be 

 produced at all. Thus, unless the rose, pea, and walnut second crosses are 

 produced from the first-cross walnuts in some way which allows an extra 

 comb to be produced ex nihilo, the assumption that rose and pea combs are 

 each due to single factors must fail. 



Consider next whether the assumption holds when tlie case is dealt with 

 on the presence and absence theory. According to Professor Batesou's sixth 

 paragraph, the constitutions of the four combs, walnut, rose, pea, and single, 

 are BBPP, BRpp, rrPP, and rrpj). It must not be forgotten that the small 

 letters merely represent the absence of the factors represented by the large 

 ones. They are merely helps to tlie memory, and unless as such might as 

 well be absent. 



In the case of the single comb, rrpp indicates that it is produced without 

 the assistance of RR or PP. By what, then, is it produced ? It must be 

 produced by something, and since RR and PP are both absent, that some- 

 thing must be separate and distinct from both. Causes that are absent can 

 have no hand in producing effects that are present. A cause, by being absent, 

 may allow another cause which it previously obstructed or whose effect it 

 obscured to have eft'ect, but the essential cause of this effect is the one wliich 

 is present. There being no symbol set down to represent the factor or 



3p2 



