MUTATION IN MATTHIOLA ANNUA, A MENDELIZING SPECIES 379 
case, even in the later generations. With all the other types, a large 
part of the progeny, usually more than one half, always belong to the 
type ("Snowflake") from which the mutant types were originally 
secured. 
Possible explanations of this peculiar transmission of the mutant 
types will be discussed in a paper now in preparation, and cannot be 
adequately considered here; lower viability of the mutant types, and 
linkage with the factor for the less viable single-flowering type^ are 
obviously concerned in some cases. The point to be emphasized here 
is that this peculiar behavior occurs in a species which, as to certain 
other factors, is typically Mendelian." 
A brief characterization of eight of the mutant types, including all 
that have been proved to be hereditary, will be given. It should be 
noted first that the foundation stock consists of one variety only, a 
very uniform white-flowered glabrous "double-throwing" form, known 
as "Snowfiake." As with other double-producing stocks, all the 
single-flowering plants are heterozygous for *'doubleness," pro- 
ducing about fifty percent^ of double progeny, while the doubles are 
totally sterile. The fact that the doubles form about one half of 
each generation, rather than one fourth, is due to the fact that all 
functional pollen is doubleness-carrying, or lacks some factor necessary 
to single (or normal) flowers. 
The early type, which was described in Annual Report 8 of the 
American Breeders' Association, differs from Snowflake (figs, i, 2 and 3) 
mainly or entirely in size-characters and earliness of flowering. The 
original early mutant was heterozygous. Twenty of its progeny 
have been tested; 4 of these were probably pure early, and 7 were 
obviously pure Snowflake. Presumably the mutation occurred in 
one germ-cell, which then united in fertilization with a normal Snow- 
flake germ-cell. In the absence of complications, such a mutant 
would be expected to reproduce its type in about 75 percent of its 
progeny — as actually occurred with this type. 
In striking contrast to this case, all the other mutant types identi- 
fied are marked by peculiarities of leaf-form and of general habit, and 
no individual yet tested has proved homozygous. 
2 The single-flowering plants appear somewhat less vigorous, and less resistant 
to some unfavorable conditions, than the double-flowering ones. 
3 There is the usual slight excess of doubles; 7,310 progeny of Snowflake parents 
included 53.037 percent of doubles. 
