56 Mutations and Evolution. 



in which the origin of new divergent characters is now or has 

 recently been taking place. 



Turning now to the recorded cases of mutation in the literature, 

 they form such an array that it would be a colossal task to attempt 

 even to enumerate them. The condition is so common in flowering 

 plants that it may be considered exceptional to find a species 

 without any mutational varieties. A few instances will be selected, 

 almost at random, for mention here. First we will consider 

 doubling. 



Doubling. 



The gardeners' tradition that "doubling" or the transformation 

 of stamens into petals, 1 is a result of cultivation has long been dis- 

 proved. It is evident from the records that doubling of flowers 

 occurs "spontaneously" both in wild and cultivated species. It is 

 a typical mutation, although the completeness of the transformation 

 of stamens into petals, and the associated changes in the flower, 

 may vary in different cases. Breeding experiments have shown 

 that the double condition is in some forms a Mendelian dominant, 

 but more usually a recessive. Bateson (1909, Chap. XI) has 

 considered the cases studied before 1909. The work of Miss 

 Saunders on the inheritance of doubleness has been most ample, 

 and some of her results may be summarized here. Taking the 

 simpler cases first, she finds (1917) that in the Welsh poppy, 

 Meconopsis cambrica, doubleness is dominant, the P a from a cross 

 containing three doubles to one single. The doubleness results 

 from a variable degree of petalody of the andrcecium and gyncecium. 

 In the hollyhock (Althcea rosea and A . fie ifolia) the F l is intermediate 

 and the F u gives the 1:2:1 ratio, i.e., neither condition dominant; 

 in carnations (Diauthus caryophyllus) doubleness is a simple 

 dominant, 2 while in sweet william (D. barbatus) singleness is 

 dominant and the F 3 from a cross contains three singles to one 

 double. 



In Chelidonium majus Sax (1918) finds that doubleness is 

 apparently a simple recessive, but the F 3 gives a continuous series 

 from singles to full doubles. Statistically considered, there is much 



1 Doubling may also occur, as in Fuchsia, by an increase in the number 

 of petals without any change in the stamens, or it may result from change of 

 carpels to petals, or from all these conditions combined. 



* According to the breeding work of Norton and of Batclielor the doubleness 

 of carnations appears to be of two distinct types or degrees, full doubles and 

 standard doubles, the latter having some stamens. Full double x single 

 gives an F, which is standard double, and an F, with the three types in the 

 ratio 1:2:1. Miss Saunders finds, however, all degrees of doubling in the 

 OD's and OR's, which are therefore indistinguishable. 



