332 BOTANICAL GAZETTE [NOVEMBER 
‘‘Presence and absence” came into use in the first place, simply as 
a convenient method of expression to avoid the confusion which 
arises when the same dominant character is described as an alterna- 
tive of several different characters which are hypostatic to it, and 
which may themselves be present or absent in any particular 
instance. The very general applicability of this mode of expres- 
sion naturally suggested to various writers (Hurst 18, SHULL 27, 
etc.) that it might have a more fundamental significance than merely 
as a convenient form of description. These authors considered it 
simpler and more practical to suppose that the heterozygous genes 
are unpaired, and that the “absence” of a character? is unrepresented 
by anyinternal unit corresponding with the gene which determines the 
“presence” of that character. The “presence and absence” hypothe- 
sis need not be associated, however, with the conception of unpaired 
determiners in the heterozygote, for in any pair of organs there may 
be present a function or feature in one member of the pair which is 
absent in the other member, or both members may be alike in kind 
but different in quantity or activity, the differential between the 
two being in this case the determiner of the alternative characters 
involved. This excess in one member of the pair would be present, 
of course, in that member only, and must be absent in its mate. 
Whether the hypothesis of unpaired genes or that of paired 
genes represents the true condition in any particular instance, 
and whether the absence of a character is absolute or only rela- 
tive, will not interfere in the least with the use of “presence 
and absence” as the most convenient method of stating a great 
majority of the alternative characters with which the student of 
heredity has to deal. For the application of these different phases 
of the “presence and absence” hypothesis to the sex problem in 
Lychnis, attention is directed to the following table: 
? It is to be regretted that some writers have misconstrued the meaning attached 
by most geneticists to the expression “absence of a character.” The absence of the 
Angora character in cats, rabbits, ete, -» does not result i ina hairless animal, vee one 
with short hair. In Ocenothera ie event 
the production of Aaeeg in the amount and localization characteristic a 0. 
rubrinervis (see Gates, R. R., Studies on the variability and heritability of pigmenta- 
tion in Oenothera. "Deltech Tid. Abst. Vererb. 4:337-372. 1911). 
