THE GERM-PLASM THEORY 309 



suits of hybridization. Thus if the position of a 

 newly discovered factor is determined by comparison 

 with another particular known factor, it is possible 

 to *' calculate the results for all other known factors 

 in the same chromosome." Morgan's ideas regard- 

 ing the organization of the chromosomes coincide 

 with those expressed by Weismann in one respect, 

 that is, they are assumed **to have definite structures 

 and not to be simply bags filled with a homogeneous 

 fluid." Wilson (1912, p. 63) also regards the chro- 

 mosomes as "compound bodies, consisting of differ- 

 ent constituents which undergo different modes of 

 segregation in different species." 



Students of genetics now consider the individual 

 as built up of a number of unit characters represented 

 in the germ-plasm by factors, and when two different 

 germ-plasms unite (amphimixis) the factors do not 

 mix, but remain uncontaminated. The germ-plasm 

 of offspring which develop from fertilized eggs is 

 supposed to consist of an assortment of factors 

 brought about during synapsis and reduction as indi- 

 cated in Fig. 84. The factors (or genes) in the germ- 

 plasm occur in pairs called allelomorphs,^ and one of 

 the pair may be regarded as dominant, the other re- 

 cessive, as, for example, the yellow and green colors of 

 pea seeds. Thus the appearance of the individual 

 depends upon the character of its dominant factors. 

 Any attempt to account for the origin of new species 



1 According to some investigators, especially in England, the presence 

 of a factor should be considered one allelomorph and its absence as the 

 contrasting factor. 



