76 The Journal of Heredity 
linked, the deviation from 50% (inde- 
pendent inheritance) of 29.2 + 3.4 be- 
ing of such a magnitude that it would 
not be expected to occur by chance 
more than once in millions of trials. 
Moreover, there was in this back cross 
no great deficiency of tassel ear to mask 
the results, since the normals were to 
the tassel ears as 53 to 43. Again, the 
numbers of all the several classes were 
very close to expectation on the basis 
of the crossover percentages noted. Of 
the 96 plants, 50 were non-crossovers, 
' 44 single crossovers, and 2 double 
crossovers. 
Unfortunately there are no data 
available at present with respect to the 
possible relations of Ts ts with B b and 
Lg lg. There are, however, back cross 
data including no less than 3,700 plants 
involving P p and Lg lg, and 2,600 in- 
volving P p and B 6, all without any 
indication of linkage. It follows, there- 
fore, that tassel seed and tassel ear are 
not only distinct genetically as well as 
morphologically, but that they belong 
to distinct linkage groups. 
Identifying the Double Recessive, 
Tassel Seed Tassel Ear—lIt is not 
known what sort of plant the double 
recessive, tassel seed tassel ear, will be. 
There is available abundant material, 
in some of which ts ts te te should ap- 
pear next season. If it should prove 
to be like one of the types described 
in this paper. tassel ear for instance, 
a9 3 :4 relation should be found to 
exist between the three phenotypes. 
Ordinarily, in such a case as this. it is 
necessary to conduct further breeding 
tests in order to distinguish the pheno- 
typically alike, but genetically different 
single and double recessives. But such 
tests might here encounter serious diffi- 
culties. The most likely procedure, in 
case the double recessive is not distin- 
guishable from one or other of the sin- 
gle recessives, is to cross random sam- 
ples of the recessive plants with both 
heterozygous tassel seed and_hetero- 
zygous tassel ear. This would involve 
considerable difficulty unless two true 
ears or one ear and the terminal in- 
florescence develop on each plant, a 
thing hardly to be expected in plants 
so weak as tassel ear. Of course it 
would doubtless be possible to make up 
the two classes of heterozygotes so that 
they differ from each other and from 
the recessives by dominant aleurone or 
endosperm characters. A single ear of 
each recessive could then be pollinated 
by both heterozygotes and the resulting 
seed separated into two lots corre- 
sponding to the two heterozygous par- 
ents. But all this would require much 
time and no little effort. 
Fortunately, no such tests should be 
necessary in the particular case under 
consideration. The known linkage rela- 
tions of tassel seed and tassel ear with 
other characters should make the solu- 
tion of the problem much less difficult. 
To emphasize the aid that some knowl- 
edge of linkage affords in such a prob- 
lem as this is the only excuse that the 
writer can plead for this attempt to 
cross an apparently difficult bridge be- 
fore he is sure that such exists. It 
will not be difficult to introduce both P p 
and B b into the cross of tassel seed and 
tassel ear. Any resulting pistillate 
flowered plant with colorless pericarp 
is almost certain to be ts ts, and there 
are about four chances in five that any 
pistillate flowered plant having the fac- 
tor of the pair B b present in the tassel- 
ear parent of the tassel-seed tassel-ear 
cross will also be fe te. 
