58 Mutations and Evolution. 



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 absent 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 Oioscorides. The first record of the double stock 

 appears to be in Dodoens* herbal (1568). This gives 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.)* 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). 



