356 MISSES K. FOOT AND E. 0, STROBELL : RESULTS OF 



I£ we examine the results of our experiments in the light of Mendel's law 

 of heredity, we find that the genital spot does not behave as a Mendelian 

 unit. Professor Punnett (1911) defines a unit-character as follows : "Unit- 

 characters are represented by definite factors in the gamete which, in the 

 process of heredity, behave as indivisible entities, and are distributed 

 accordiup- to a definite scheme. The factor for this or that unit-character is 

 either present in the gamete, or it is not present. It must be there in its 

 entirety, or be completely absent." (Page 42.) 



Whatever determines the genital spot in these hybrids, it cannot be an 

 indivisible unit-factor, which is " present in its entirety " or is " completely 

 absent,'' for the genital spot is not present as a whole, or completely absent. 

 If we speak of it in terms of Mendelism, we must say that it is the result 

 of a number of unit-factors, for in the hybrid males of the Fi and Fg 

 generations in which a spot can be identified, it is present in every degree of 

 intensity, from a mere indication of a spot, to that of the Fg generation 

 which is quite as conspicuous as the spot of a pure variolarhis. 



Neither the spot nor its absence is dominant in the Fi hybrids. There 

 is certainly an absence of dominance in this Fi generation. Of the eleven 

 Fi male hybrids, 2 have no spot (photo 7) : 4 have a spot so faint that it is 

 barely visible (photos 8 and 14 and one fdnned specimen) ; and 5 have a spot 

 about one third as pronounced as that of a pure variolarhis (photos 9, 10, 

 11, 12, and 13). 



It is evident also that the spot of these Fi hybrids is not a true blend, 

 for only one parent is represented by the two specimens that have no spot, 

 and there is quite as much variation in the size and intensity of the spot 

 of the remaining nine specimens as is found in any nine intermediates of 

 the F2 generation. 



The F2 generation shows apparently a greater variability than the F]' 

 generation, for in the former both extremes are represented, some of the 

 males having a spot as pronounced as that of pure variolarius, while some' 

 have no spot whatever, and the remainder have the spot in varying degrees 

 of size and intensity. These facts may be of value as offering a test such 

 as Castle (1911) has suggested, by which it may be possible to decide whether 

 the results can be classed with the Mendelian type of inheritance, or with 

 that described as a " non-Mendelian, non-segregating type of inheritance/' 

 Castle says : " There is one means by which we can determine with certainty 

 whether, in a particular case of seemingly blending inheritance, segregation 

 does or does not occur, namely by comparing the variability of the Fi 

 and Fg generations. If segregation does not occur, Fg should be no more 

 variable than Fi, whereas if segregation does occur, Fg should be more 

 variable." (Page 137.) 



Although the Fg generation of our Euschistus hybrids shows more varia- 

 bility than the Fi generation, the value of this as proof is weakened, if not 



