AN ANALYSIS OF THE EFFECT OF SELECTION. 45 



modifiers {i. e., modifiers producing only small effects) will account 

 for all these facts, with a single exception. Three families were ob- 

 tained from F2 plants that must, on the two-factor view, have been 

 of the same constitution. These plants were heterozygous for one 

 pair of genes only. They produced, in F4, the same type of later 

 constant (homozygous) families, but differed slightly in the flowering 

 times of the earlier constant families produced. According to Ho- 

 shino's view, if the earlier types differed the later ones should have 

 differed in the same direction, because they must have received the 

 same "secondary modifiers." This objection is not vaHd, for specific 

 modifiers that act only in the presence of certain other genes are well 

 known (see especially Bridges, 1916), and are sufficient to account 

 for the differences observed. This argument is the only one that 

 Hoshino gives to support his conclusion that contamination must 

 have occurred. We must then conclude that the case does not furnish 

 positive evidence for contamination, since it is exphcable without re- 

 course to that hypothesis.^ 



11. Unspecified Case in Swine. 



This case is cited by Castle (1916&, p. 215), but no references or 

 authorities are given. It appears, however, from the legend under fig- 

 ure 93 (opposite p. 139) that the belted character is the one referred to. 

 The only data bearing on this case that I have found are presented by 

 Spillman (1907), and consist of information supplied largely by prac- 

 tical swine-breeders. Spilhnan himself interpreted the case as one in 

 which two factor-pairs are involved. The data also suggest the pos- 

 sibiUty that we are deahng with a case of ''imperfect dominance" simi- 

 lar to those in poultry. At best, the data are meager and indefinite. 



12. Variegated Pericarp in Maize. 



The paper of Hayes (1917) referred to above should be studied 

 in connection with those of Emerson, particularly his full paper (Emer- 

 son, 1917), dealing with the same character. These two workers have 

 shown that there is a remarkable series of multiple allelomorphs in 

 this case, and Emerson has shown very clearly that some of these 

 allelomorphs mutate quite frequently— the only estabUshed instance 

 of the sort. _^_ 



iWe are not here directly concerned with Castle's contention that Hoshino's results prove 

 the effectiveness of selection within a pure line. I can not, however, refrain from a few comments 

 on that contention. Castle states (1916rt, p. 324), in connection with the differences in fiowermg- 

 time between the offspring of early and late flowering sister-plants: "From long experience in 

 studies of rats with such small differences as are here indicated I have no hesitation in concluding 

 that fluctuating variation of genetic significance is here in evidence." One wonders how ex- 

 perience in dealing with differences in pigmentation in rats can give an observer special ability 

 in determining by inspection the significance of three- tenths of a day diffeience in the flowering 

 time of peas. With respect to Castle's calculations from Hoshino's data, it may be pointed 

 out that the greatest favorable difference recorded, 1.27 days, is incorrect, and should read 0.26 

 day. In view of the fact that there is no guarantee that the material used was homozygous, 

 I have thought it scarcely worth while to recalculate all the differences, or to determine their 

 probable errors; but it is certain that the probable error of each difference is of the same order of 

 magnitude as the average difference itself, i. e., about 0.3 day. 



