MUTANTS AND HYBRIDS OF THE OENOTHERAS. 33 



nervis, by which it was able to give rise to nanella, no longer exists. 

 The loss of mutability has been noted to be accompanied by an acqui- 

 sition of the Mendelian procedure in the hybridization of these two 

 forms. (De Vries, 1903, pp. 458, 460.) 



The discovery of single plants presumably derived from an ances- 

 tral mutation, or of a few plants as mutants from a parent, suggest 

 that in some instances the period of mutability of a species may 

 include only a single season, and these brief periods may recur at 

 intervals concerning which information is totally lacking. In the case 

 of Oenotheras, however, the first mutants in bloom were found in 1887, 

 which shows that the parents from which they were derived perfected 

 their seeds in 1885. The recurrence of various mutants has been noted 

 in every succeedingyear, including 1904, and it is to be seen, therefore, 

 that this species has been in a mutable condition for twenty years. 

 How much earlier mutants have been formed than the date given 

 above cannot be surmised. The continuance of the capacity for muta- 

 bility is open to actual observation, however, and it may be possible 

 within fthe next few years for the botanist to actually witness the 

 closing of the mutative period in this plant which has furnished 

 material so rich in practical and theoretical results. The procedure of 

 O. lamarckiana is supposed by De Vries to be similar to that which 

 has been followed by Draba and Viola in the productions of the 

 swarms of species now recognized. (De Vries, 1905.) 



During the cultures of 1902- 1903 O. lamarckiana, O. nanella, and 

 O. rubrinervis were grown as biennials for purposes of comparison 

 with the behavior of other species. During 1904, however, seeds were 

 sown in the propagating houses about the first of the year and the 

 plantlets, after being properly transferred from smaller to larger pots, 

 were placed in the soil in the experimental grounds in the latter part 

 of May. No marked difference between the two series could be 

 detected. It was noted that 0. gigas, however, has more thoroughly 

 established itself in the biennial habit and that not half of the plants 

 grown as annuals actually produced flowers or seeds in 1904. 



The estimation of the general hardiness or fitness of the parental 

 form and of the mutants, with a view to the determination of their rel- 

 ative value if thrown into a competitive struggle for existence, is not 

 to be too lightly made. O. lamarckiana has not spread over any part 

 of North America having the climate of New York, and its cultivation 

 in this locality must bring into contact many factors inoperative in its 

 natural habitat. Tests made under such conditions must be accepted 

 most guardedly. A general description of some of the more striking 

 characteristics of the various forms will be of some value, however. 



