344 LINDSTROM, GENETICAL RESEARCH WITH MAIZE 
ked tendency for the production of offspring with solid red ears (with 
red cobs as well). Since the genetic relations between solid red and va- 
riegated pericarp are well known the situation offers a splendid source 
of material for a study of the mutation problem. 
As has been pointed out in the section dealing with pericarp and cob 
colors, the variegated type has been fitted into a multiple allelomor- 
phic relation. Actually there are known at the present time at least two 
distinct types of variegation, the so called medium-and light- variega- 
ted types. A dark variegated type is also known, although less work 
has been done with that. 
The multiple allelomorphic series of the pericarp and cob colors that 
serve to explain the variegation problem can be listed in their epistatic 
order, as follows: — 
Pr" — red pericarp and red cob. 
Pm» — medium variegated pericarp and cob. 
Pe — light + 3 ae. or 
pv’ — white pericarp and cob. 
The last named type is recessive to any of the others. 
According to Emerson (1914, 1917 and 1922) either type of variega- 
gation P”” or P” can mutate to the solid red pericarp (and cob) condi- 
tion P'”. This is a change form a recessive to a dominant type. The re- 
verse mutation also has been noted but much less frequently. — 
The mutation noted above occurs apparently at any stage in the de- 
velopment of the plant. When occurring early in the life history, the 
entire ear of an otherwise variegated variety may become solid red. 
When it happens later, only a certain portion of the ear, or only a few 
kernels, or only a part of a kernel may show the change. The chances of 
the mutation being inherited are greater if the change has occurred 
early, presumably in time to strike the germ plasm. Later mutations 
may affect only the epidermal tissue and accordingly the mutation will 
not be transmitted to the progeny. 
A noteworthy phenomenon of the situation is that a heterozygous 
variegated ear, as PAY PPP, most certainly mutates more frequently 
than a homozygous one, P”” P", altho there are two variegation ge- 
nes as sources for mutation in this case. When such a heterozygous 
type undergoes mutation the P”” gene is always the one affected, never 
