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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
less parts was invariably sharp but usually somewhat irregular. The 
correspondence in outline between the colorless aleurone and the under- 
lying waxy endosperm was strikingly exact irrespective of the number of 
spots per seed or of their irregularity (fig. i ; 7, /, K, L). The waxy endo- 
sperm was found to extend to varying depths, the smaller spots often being 
more shallow than the larger ones (fig. i; K, L). Moreover, the larger 
waxy parts often exhibited a somewhat irregular outline in cross-section 
(fig. I, K). It is perhaps possible that the three seeds noted as having 
corneous endosperm under the colorless aleurone had in reality a very 
shallow layer of waxy endosperm, but this is not likely since in neither 
case did the colorless spot include less than about one fourth of the entire 
area of the seed. 
The writer has examined three aberrant seeds involving C c and Wx wx 
from cultures other than his own and in each case the colorless aleurone was 
directly over waxy endosperm. The seed described by G. N. Collins (1913), 
from Fo of a cross of white waxy with pollen of colored non-waxy types, in 
which the colorless aleurone was underlaid by waxy and the colored part 
by corneous endosperm, involved, it is now almost certain, C c with Wx wx. 
Collins's published F2 records leave no doubt that he was dealing with a case 
of linkage between waxy endosperm and some aleurone factor. The cross 
certainly did not involve the aleurone factor pair I i, for the colorless 
condition was recessive. Aleurone-color factors A a (Bregger, 191 8) and 
Rr (Kempton, 1919) are. now known to be inherited independently of 
Wx wx, so that C c is the only known factor pair that could have been 
involved. Since, however, Collins's case appeared in F2 and since there 
is about 25 percent of crossing-over between C c and Wx wx, there is no 
certainty that both C and Wx were in one chromosome and c and wx in 
another. 
The evidence derived from crosses involving the linked genes C-Wx 
and c-wx points conclusively — in so far as genetic evidence can be regarded 
as at all conclusive with respect to cytological behavior — to some aberrant 
chromosome distribution, perhaps non-disjunction, as the cause of most 
cases of aberrant endosperm development; but the three instances noted 
above of corneous endosperm underlying colorless spots of aleurone suggest, 
though they do not prove, that very rarely somatic mutation may be 
responsible. 
Evidence from other linked factors in addition to C c and Wx wx 
would be of great value as tending to confirm or contradict the conclusion 
here drawn. A number of such linkages are now known. In addition to 
the linkage of / with Wx wx, inferred, as noted earlier in this paper, from 
Hutchison's data, Hutchison has found both / i and C ^: to be closely 
linked with shrunken endosperm, Sh sh, and Dr. E. G. Anderson (un- 
published data) has noted linkage between a factor pair for blotched 
aleurone, Bh bh, and the pair Y y for yellow endosperm. 
