) I I II 
6 Research Bulletin No. 2 
absence notation has come into general use. In truth one must 
accept a reversal of de Vries* views, for the presence and absence 
notation is based on the fact that the hereditary transmission of 
a factor can only be determined when the factor is present in one 
of the parental gametes and absent from the other. 
A second reason for limiting the operation of Mendel's law 
was the earlier misconception of the importance of the phenom- 
enon of dominance. This reason shortly disappeared when it 
was found that perfect dominance was the exception rather than 
the rule and that cases where dominance was entirely lacking 
were frequently found. 
These were important concessions that contributed much 
toward recognition of the importance of the Mendelian concep- 
tion of heredity, but the main stumbling-block to Mendelism lay 
in the comparative frequency of quantitative variations. The 
variations whose behavior in crosses yielded to a simple factorial 
interpretation were all qualitative in character. They could 
reasonably be regarded as being due to the presence or absence 
of something in the gamete. Such varietal differences existed 
by the score, yet their number was insignificant when compared 
with the multitude of variations expressed as differences in size 
of organs common to the individuals under consideration. Many 
of these differences, it is true, were fluctuations due to environ- 
ment which were non-heritable,* but the remaining transmissible 
variations were legion. About three years ago, however, a hy- 
pothesis was proposed which would bring even this broad category 
of facts under the scope of the law of unit-factor segregation and 
recombination. The experimental data upon which this hy- 
pothesis was then based and the data that have been collected 
subsequently are comparatively few, yet the fact that the experi 
ments of several independent investigators have been corrobora- 
tive in every detail makes it plausible to believe that its main 
contention will soon be established beyond a reasonable doubt. 
If this statement be granted for the moment, one might hazard 
the suggestion that the probable limits that circumscribe Mende- 
lian phenomena really do coincide with the limits within which 
transmissible character potentialities are transferred by typical 
sexual reproduction. In other words, Mendelian phenomena are 
in some way bound uj5 in and coincident with that preparation 
of the reproductive cells called maturation and their subsequent 
fusion to form a new organism. This, it is thought, is an ad 
missible induction from the conspicuous diversity and profusion 
* It has been shown that if adaptive responses are ever heritable, the 
phenomenon is so rare that it may be neglected in experimental pedigree 
cultures. 
