46 Mutations and Evolution. 



Cat. under the name Lysimachia corniculata non papposa, Virginiana 

 major, flore sulphured. 1 It must then have been appearing as a 

 mutation in the original stock brought from America. Other wild 

 American self-pollinated species recently brought into cultivation 

 have been shown to be doing the same thing, i.e., producing 

 mutations with varying frequency. We must recognize that the 

 germ-plasm of a species is a vast aggregation of units, among which 

 complicated relationships arise which express themselves in 

 throwing off at intervals new forms. 



The frequency with which the mutations in CE. biennis appear 

 has been studied by de Vries (1915b). He grew 8500 plants from 

 the pure line of Stomps, derived from a single wild plant from 

 which they were descended in the third and fourth generation. 

 They included 8 dwarfs (mut. nanella) or 0'1%, and dwarfs also 

 occurred in later generations. The population of 8500 also 

 contained 4 semigigas, or 05%, i and 27 sulfurea, or 0-3%. The 

 latter appeared among the offspring of all seven parent plants. 

 This gives a total of 39 mutations, or 0'45%. This is a lower 

 percentage than in CE. Lamarckiana, but much higher than in 

 Drosophila. Cultures of CE. biennis sulfurea from four of Stomps' 

 mutants also gave two dwarfs among over 1000 plants which 

 flowered. These give the race CE. friennis mut. (1913) sulfurea mut. 

 (1914) nanella. In this connection de Vries also obtained two 

 other mutations from crosses. CE. lamarckiana x CE. biennis 

 nanella yielded 55 plants, which had the characters of lamarckiana 

 X biennis, except one Inta mutant. Again, in the cross CE. biennis 

 semigigas X CE. biennis, he obtained 19 plants, 1 dwarf mutant, 

 10 biennis with 14 chromosomes, and 8 of a new type (described else- 

 where) with 15 chromosomes. The appearance of two uniform 

 types in this cross is significant, for it shows that the meiotic 

 processes were taking place so as to reduce the chromosome 

 number in the gametes to 7 or 8. Moreover the fact that the 

 15-chromosome type was uniform indicates that the same chromo- 

 some must have been the extra one in every case. 



This brings us to the meaning to be attached to the term 

 parallel in connection with mutations. It is obvious that each 

 mutation of a given type is parallel to every other of that type. 



1 Sec Mutation Factor, pp. 66. 158. The fact that the early writers, 

 although they recognized sulfurea, found no other variations of CE. biennis, 

 shows that it was as uniform then as it is now. 



1 If mut. gigas. appeared only from the union of two diploid gametes, its 

 frequency should then be about 1 : 4,000,000. 



