ON THE NATURE AND BASIS OF HEREDITY. 183 



It is claimed that the peas form an exception, as their organs of fertihzation 

 are protected by the keel. But it is admitted that "even here there have arisen 

 numerous varieties during a cultural period of more than 1,000 years; these 

 maintain, however, under unchanging environments a stability as great as that 

 of species growing wild." 



Pigeons jircsent the following advantages over peas in crossing: (1) In peas we 

 can not put the individual to more than one test. In pigeons we can test an indi- 

 vidual over and over again, one year after another; we can test it with different 

 individuals of its own kind or by various crosses. This advantage enables us to see 

 that the individual carries different (not necessarily "pure") germs. (2) Pigeons 

 present phylogenetic stages (ageing), so that an individual gives us two well-marked 

 phases for study — one in the first plumage and another in the second or adult 

 plumage. (3) The characters, although more complex, are more definite, and give 

 more than one differential. These points probably more than counterbalance the 

 reality involved in the objection raised by Mendel and by Bateson that a multitude 

 of characters might be an obstacle to discovering Mendel's law." (W 10) 



De Vries's mutations'" make it impossible to investigate. Premutations are as 

 immutable as mutations, and they are not supposed to come in gradually, but by a 

 complete and sudden transformation. 



Mendelism — pure germs, segregation, etc. — ignores the real thing, namelj^, 

 genn-variatiou, and refers all changes in characters, in color for example, to germs 

 introduced somewhere in the parent stock. It speaks of reversion, etc., as due to 

 the cropping-up of old germs that have suddenly come into the field." Changes due, 

 for example, to weakening by inbreeding are all declared to be "segregation." 



WEAK GERMS AND IRREGULARITIES IN DEVELOPMENT.'^ 



White color. — Most students of genetics treat white as a character. Now, in 

 albinos or partial albino pigeons and pheasants we have clear evidence that the 

 presence of "patches of white" mean only that the organism is too weak to bring 

 its development to the point of forming the normal color-pattern. 



If this pattern represents many specific characters, as it does, then it is evident 

 that in the case of a particular albino pheasant, '' to be described in the next para- 

 graph, we have a lack of energy to carry out development, for this same albino 

 gradually, in the course of 2 years, acquired nearly the full normal color with all the 



" Why is Mendelism found only in hybrids between "closely related" forms? We may observe that in closely 

 allied species each parent represents nearly all of the characters found in the two species. If the two species stand wide 

 apart, then each parent represents only a fraction thiit mijilif ili scml lo iii-.nly i]iir-Ii:ilf in extreme cases. In other 

 words, the hybrid represents the sum of the diffi n >il cIlh nrh is; ,-./., Mippn-r il):,i in two close allies each has 10 

 characters, 9 of which are common; then the sum of tlir ihff,r,i,l cIi.iiniIi ; - wciil.l l.c '.I + 2 = 11. Suppose each 

 has 10 characters, 5 of which are common. Then the sum will be 5 + .3 + .J = lo- yuppuse only 1 is common; then 

 the sum will be 1 + 9 + 9 = 19. The sum will increase as the number of common characters is smaller. Although 

 each species has only 10 characters, the number of characters to be represented in the hybrid will vary from 11 to 

 19. (X, Z, W) 



'" De Vrie.s's test of species by cross-fertilization can not be applied among the fungi; in many of these there is 

 no fertihzation, and when there is, it is self-fertilization. Among bacteria species can often be distinguished only 

 by physiolofiieal means. 



" It is ]iro)i:iI.ly tnir tli.il tl,,' .:,.,,•;,- rli iivtos throughout the whole life cycle. 



"Tlii':iii:ni,u^' nl o! il.j. . i i I ' I nling is that of the editor. The descriptions and headlines are solely 



those of tho :iullinr: I Im' II : ■,. ,, .:.^'r ! i -Editor. 



"Many i:im - :iiv I n n; i in i '. mts assuming male plumage. No cock pheasants were ever known 



to revert to female garb. 

 13 



