Inheritance of Rest Period of Seeds in the Peanut


in which one-half of the genetic range is non-effective or how
such a system became established. It is equally difficult to
understand how varieties of the cultivated species came to be
separated into two distinct groups. An environment which
favored the short or no rest period type would probably allow
accumulation of mutations in either direction back of the ger-
mination threshold where selection pressure must be very weak.
A variable (tropical?) environment where growing conditions
prevailed continuously except for rare and irregular intervals
would favor a type which usually required no rest period but
required rest periods of varying lengths in a small proportion
of seeds to bridge unfavorable periods. The present system is
remarkably well adapted to provide that type, regardless of
degree of inbreeding. It would be disadvantageous if zero rest
period were a minimum genotype and hence a rare combination.
More dormant types may be relatively recent developments from
the above system segregated in response to increasing regularity
of unfavorable periods alternating with growing seasons as the
plant migrated to higher altitudes or latitudes.
 No parallel cases of the rest period type of inheritance have
been reported and this type is not expected to appear with
vital characters nor with characters upon which selection is
never reversed. However, a sudden shift of environment with
no reversal of selection may produce the situation temporarily
even with characters as vital as reproductive capacity. A cross
of two heterozygous strains of corn (Zea mays) under observa-
tion by the writer shows the rest period type of inheritance
of tillers per plant under conditions where adapted varieties
produce about 30 bushels per acre. The non-tillering strain pro-
duces a single small tiller on 7 percent of its plants and none
on the remainder. There can be little doubt that in a more
favorable environment the same strain would produce tillers
on nearly every plant and that the highly skewed distribution
of F2 plants with mode in the zero class would be transformed
to near normal type. Similarly a cross of high. and low produc-
ing strains of a grain crop might be shifted to an environment
where the low producing strain and a large proportion of F2
plants produced no grain. The usual type of quantitative in-
heritance would be transformed to the rest period type but a
return to the normal type would eventually be effected by selec-
tion if the new environment continued.