324 BOTANICAL GAZETTE [OCTOBER 
veloped awns on both flowering glumes, a densely pubescent rhachilla, and 
dense pubescence at the base of both fertile florets. The “intermediate”’ base, 
as would be expected, is associated with an intermediate development of the 
other characters. Thus, in some spikelets the first floret has a medium sized 
awn, but the second has none; likewise, the first floret has pubescence at the 
base, but the second is glabrous. It is on the basis of differences between the 
first and second florets that SURFACE is able to correlate 7 putatively distinct 
characters with the “cultivated” type of base, but those whose view of 
Mendelian inheritance is less formal than the author’s will wish very clear 
evidence Fela admitting them as distinct. SuRFace himself has suggested, 
following Nitsson-ExLe, that characters may be genetically present in an 
individual, but not manifest because of environmental conditions. In some 
strains of oats, for example, awns are potentially present, but develop only 
under certain external conditions. at is true of a population, acted upon 
by varying environmental factors, may equally well be true of homologous parts 
of a single individual, conditioned in development by their position on that 
individual. : 
Turning to a concrete case, the spikelet of Avena is composed of 2, or at 
most 3, fertile florets, presenting a gradation from the first, which is large and 
in every way the most highly developed, to the third, which is ordinarily a 
sterile or even vestigial structure. In a reduction series composed of so few 
members, and with so steep a gradient, we. have ideal conditions for a variable 
character to be manifest in the first member and latent in the second. At 
any rate the reviewer would look for a physiological rather than a genetical 
explanation for the situation as regards awns and pubescence in the spikelet 
of Avena. If the first flowering glume is awned, it is a fair assumption that 
the second is potentially the same, even though its position be such that mani- 
festation of the character is a physiological impossibility. Perhaps an under- 
lying basis for the whole group of correlations might be found in the diminution 
of the vascular supply between the base and apex of the spikelet 
In addition to the characters showing perfect correlation, SURFACE dis- 
covered two pairs of characters showing partial linkage. The factor for 
pubescence on the back of the first flowering glume showed linkage with the 
factor for black color of the glume, and the pubescence of the back of the 
second flowering glume showed linkage with the “wild” base. In respect to 
these characters the data are too involved to be repeated here, but as inter- 
preted by SuRFACE they show (1) that the presence of pubescence is a dominant 
character in the case of the first flowering glume, but a recessive character in 
the case of the second glume, and (2) that the factor for pubescence of the 
lower glume is a basic pubescence factor, in the abscence of which the factor 
for pubescence of the second glume is without effect. The bare facts upon 
which SURFACE bases these conclusions are as follows. The first hybrid gen- 
eration has the lower flowering glume pubescent, the upper smooth. In the 
one parent, Avena fatua, both glumes are pubescent; in the other, A. sativa, 
