426 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



of such Sterility as is in evidence in cases of physiological incom- 

 patibility in which spores and gametes are formed and in which 

 the incompatibilities appear to be largely independent of any 

 direct intracellular relations of the two parental elements in the 

 germ plasm. 



These cases suggest that the phases of fertilization involving 

 cell fusion are more properly to be regarded as being conditioned 

 by factors of cytoplasmic differentiation or general protoplasmic 

 organization, while those of synapsis and reduction are condi- 

 tioned by the mutual relations of the nuclear and cytoplasmic 

 elements involved. 



The general results of breeding indicate that when the cyto- 

 plasmic and nuclear relations are such that fertilization can occur, 

 there is, as a rule, chance fertilization between all gametes irre- 

 spective of their particular hereditary complex. Such assumed 

 behavior has been the fundamental basis of Mendelian doctrine. 

 In the production of the so-called dominants and recessives from 

 any F2 hybrid, gametes that are alike (at least in respect to the 

 characters involved) combine, while in the production of the 

 impure members of the same generation gametes that are unlike 

 are assumed to combine quite as in the production of the parent 

 Fi plants. Homozygosity and heterozygosity are generally as- 

 sumed to occur with equal chance. 



The only incompatibility, if we may call it such, that is assumed 

 to occur in such cases is that between assumed hereditary units or 

 factors at the time of the reduction division and here chemical 

 or mechanical relations are assumed to give pairing and complete 

 segregation of the elements of the pairs of allelomorphs whether 

 they both are similar (represent the same character or fraction 

 of a character), whether they are dissimilar, or whether they 

 represent the presence and absence of a character. All have been 

 assumed to segregate with quite their original integrity and value. 

 While it is becoming very evident that the general doctrine of 

 unit characters or unit factors and of jjurity of segregation have 

 at most only a rather limited ai)plication, the general results of 

 breeding have been assumed to indicate that to a certain degree 

 similarity and dissimilarity of particular germ-plasm elements 

 are not in themselves to be considered as definitely limiting 

 fertility except perhaps in cases where impotence appears. The 



