382 
HOWARD B. FROST 
The last five types described have all given considerably less than 
50 percent of mutant-type progeny. 
The small-smooth-leaved type is the smallest and weakest of all 
that have been named. Two individuals, both singles, have flowered, 
but no seed was produced. Several other forms have been named, 
but have failed to give seed; it is very probable that at least two or 
three of these are definite genetic types, distinct from any discussed 
above. In fact, it is not improbable that as many as fifteen distinct 
The Crenate-leaved Type 
Fig. 3. Matthiola plants grown in greenhouses at Ithaca, N. Y. Progeny of 
Snowflake parents. Types: one Snowflake plant at the left in each row, the rest 
Crenate-leaved mutants. Note the crenation or serration of the leaf-margins, which 
here is nearly absent with Snowflake but usually very marked with Crenate-leaved. 
genetic types have been observed, some perhaps only once among 
about 8,000 plants. 
Many Snowflake parents have given mutant progeny. The 
number of apparent mutants, under favorable conditions for germina- 
tion and growth, was about four or five percent of the whole number 
of progeny. The commoner forms appeared many times, as progeny 
of many parents; it seems probable that any Snowflake parent, self- 
pollinated, can give rise to any of the mutant types studied. It is, 
however, probable that plants of some mutant types produce other 
mutant types more frequently than does Snowflake. 
The mutant individuals are obviously not extracted pure reces- 
sives, but heterozygous dominants. Since they have occurred many 
times in cultures from selfed parents, they are not due to combination 
of complementary factors by cross-fertilization. They would seem, 
then, to be due to definite changes in the germ-plasm, changes dis- 
