14 THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 



Lastly, mutations have been observed by H. H. Bartlett 1 ) to 

 arise in 0. stenomeres, a new species of Montgomery, Maryland. 

 In the fourth generation of a pure strain, embracing 106 indi- 

 viduals, he found three aberrant types. One was a self-sterile 

 plant, the second had thick buds and short thick fruits, and the 

 third was a stout and very hairy individual with densely hairy 

 petals, which justify its new name 0. stenomeres mut. lasiopetala. 

 Hairy petals constitute quite a new discontinuous variation among 

 the evening primroses, since all individuals of 0. stenomeres, as 

 well as the allied species now being studies in this respect, have 

 petals which are glabrous, except under microscopic examina- 

 tion. 



From this list we see that at least seven species, besides 0. 

 Lamarckiana, are now known to be in a condition of mutability, 

 namely 0. biennis L., 0. biennis Chicago, 0. muricata L., 0. atro- 

 virens Bartl., 0. suaveolens Desf., 0. grandiflora Ait., 2 ) and 0. 

 stenomeres Bartl. Probably more or less numerous allied forms 

 will prove to be in the same condition as soon as they are tried 

 on a sufficiently large scale. Therefore, this mutability can no 

 longer be explained on the ground of observed or supposed char- 

 acters of 0. Lamarckiana which would distinguish this species 

 from the other types of the group Onagra. 



0. biennis L., the European type of the species, which is growing 

 wild and in large quantities in the sand dunes of Holland, where 

 it had already been observed and collected by Linnaeus, is, next 

 to 0. Lamarckiana, the most suitable for researches concerning 

 mutability. Davis says: "No wild species of evening primrose 

 has been so long under experimental and field observation or is 

 better known to the workers with Oenotheras than this plant. 

 The species has proven uniform to a remarkable degree, and it 

 would be difficult to find a type of Oenothera so free from suspicion 

 of gametic purity. The species appears to have been in Holland 

 since pre-Linnean days, and is therefore very old. As material 

 for experimental studies on mutation, the Dutch biennis seems to 



i) Bartlett, H. H., An account of the cruciate-flowered Oenotheras 

 of the subgenus Onagra. Amer. Jour. Bot. 1:226 — 243, pis. 19 — 21, 

 1914; see p. 236. 



2) Concerning the specific difference of the two last named forms, 

 which have often been considered as synonyms, see U Oenothera grandiflora 

 de l'herbier de Lamarck, Opera VI, p. 564. 



