SOME UKMAHKS ABOUT UNITS IN HEREDITY 139 



consist ill :in iilti-ratioii of the clicinism' at a special point ol a cliro- 

 mosomc. Now such alterations may l)i' more or less different, and 

 where several sucli difterences exist in a certain locus of a cliromosome 

 we have the so-called multiple allelomorphs . This rather cumber- 

 some expression ouf^'ht to be replaced — the morph ehminated. 

 »Allelofîene > seems a more neutral word. Perhaps the best expressions 

 are »multiple allelos > and »multiple allelismv, or — to be purely Greek 

 — polyullelism > . At any rate multiple allelos are (for the chromosome 

 theory) different states (chemismsl in the same locus of a chromosom<'. 

 If we consider Haur's beautiful case of three » allelos - in rej^ard to 

 chlorophyll-modifications, these corresponding > factors» may have ana- 

 logous signs, e. g. %, A, a or the like. The rich material from the Ame- 

 rican Dro.çop/H7r/-researches of Morgan's school has supplied many ca- 

 ses of multiple allelisms — most or all of them being different > ab- 

 normities» compared with the characters of the normal wild fly. 



Nilsson-Ehle's famous experiences with cereals establishing the 

 existence of »equivalent factors^ or factors acting in almost the same 

 way as to the phenotype in question, formed one of the most consi- 

 derable extensions of Mendelism. Duly understood this discovery re- 

 moves the idea of unit-characters, but perhaps the most important side 

 of Nilssox-Ehle's i)rinciple of equivalent factors is the conquest for 

 factorial analysis of the originally alleged »non-Mendelian» inheritance 

 of many so-called quantitative characters» in plants and animals — 

 Lang of Zürich was a prominent initiator of these ideas. Nilsson-Ehm:'s 

 work has also had the greatest influence on the discussion of the i)ro- 

 blem of Selection — the latest publications of our former antagonist 

 C.ASTLE best illustrates that fact. 



However, this matter shall not be discussed now. Here we wish to 

 emphasize that equivalent or analogous factors in Nilsson-Ehle's sense 

 may be regarded as the same or a rather similar state (chemism i in 

 different chromosomes. This often so-called polymerism> or liomo- 

 merism» (perhaps better »polygenism» ) must not be confused with 

 multiple allelism (polyallelism) — different states in the same locus of 

 one chromosome: polygenism on the contrary being the same state lo- 

 calized in different chromosomes! 



But however far we may proceed in analysing the genotypes into 

 separable genes or factors, it must always be borne in mind, that the 

 characters of the organisms — their phenotypical features — are the 

 reaction of the genotype in toto. The Mendelian units as such, taken 

 per se are powerless. 



