Mutations and Evolution. 
175 
factor. This does not of course explain the important fact of 
differential viability of certain types of gametes as between pollen 
and ovules. 
Miss Saunders assumes that singleness in stocks is due to the 
presence of two factors X and Y, that in the eversporting singles 
these two factors show partial coupling, and that they are both 
carried only by the ovules. Also a factor W represents colourless 
plastids, while in cream forms that breed true W is absent. There 
is also a sulphur-white race, heterozygous for W, in which W is 
present in some of the ovules but absept from the functional pollen. 
This relationship appears to be explained by coupling of W with 
either X or Y. Again, in the singles which breed true for singleness 
it is assumed thatX and Y are linked, so that in crosses with ever- 
sporting singles recombinations cannot occur. These complicated 
relationships of factors are quite in harmony with results obtained 
from breeding experiments with other organisms. 
Another feature of the double stocks is that they show greater 
viability than the singles, and hence appear in a higher percentage 
from old seed and also when the more vigorous plants are selected 
before flowering. 
The various varieties of stocks must have originated through 
mutations, and Miss Saunders (1915b) traces the historical order 
of their appearance. 
In Fuchs’ herbal (1542) the purple, red and white forms were 
already known, but Ruellius a few years earlier makes no mention 
of the red. The purple and white varieties of Matthiola incana 
date back to Dioscorides. The first record of the double stock 
appears to be in Dodoens’ herbal (1568). This is also the first 
European record of the double wallflower. Double violets are 
apparently first mentioned in a work published in 1535. 
The records indicate that the double stock perhaps originated 
in cultivation in some Dutch garden, and they show that it was 
completely double and sterile from its first appearance—no doubt a 
mutation. Sowerby (Eng. Bot .) 1 figures a hoary stock obtained 
from the cliffs of Sussex in 1806. This shows partial doubling in 
some flowers. The species must have independently developed a 
factor for doubling in this locality. 
Frost (1912) describes an “early” dwarf mutation with few 
nodes from ten-weeks stocks. It is said to behave as a simple 
Mendelian dominant, but the evidence is not very clear. 
1 See Saunders (1917). 
