. Heredity and evolution in plants . FIG. 61.—Lamarcks evening-primrose ((EnotheraLamarckiana). A muta-ting species. Cf. Fig. 62. (After de Vries.) had spread; O. lavifolia on the other hand, in a smallgroup of 10 to 12 plants, some of which were floweringwhilst others consisted only of radical leaves, in a part ofthe field which had not up to that time been occupied byO. Lamarckiana. The impression produced was that allthese plants had come from the seeds of a single mutant. EXPERIMENTAL EVOLUTION 117 Since that time, both the new forms have more or lessspread over the field (de Vries). Anoth
. Heredity and evolution in plants . FIG. 61.—Lamarcks evening-primrose ((EnotheraLamarckiana). A muta-ting species. Cf. Fig. 62. (After de Vries.) had spread; O. lavifolia on the other hand, in a smallgroup of 10 to 12 plants, some of which were floweringwhilst others consisted only of radical leaves, in a part ofthe field which had not up to that time been occupied byO. Lamarckiana. The impression produced was that allthese plants had come from the seeds of a single mutant. EXPERIMENTAL EVOLUTION 117 Since that time, both the new forms have more or lessspread over the field (de Vries). Another mutant of 0. Lamarckiana was called byde Vries (Enothera gigas (Fig. 62). The cells of thismutant have twice as many chromosomes as the FIG. 62.—Giant evening-primrose (Enothera gigas, a mutant from(Enotheia Lamarckiana, originated in 1895. Cf. Fig. 61. (After deVries.) 92. The Test of a Mutation.—The deciding test as towhether a given new form, arising without crossing froma form that has bred true for at least two generations, isreally a mutant or merely a fluctuating variant, is to seeif it breeds true to seed for the new character or characters. Il8 HEREDITY AND EVOLUTION IN PLANTS If it does it is a mutant; otherwise it is not. It is clear,therefore, that the only way the problem can be followedout is by experiment—hence the term experimental evolu-tion. The next step for de Vries to take, after discoveringthe two forms that he supposed to be mutants, was to breedthem in carefully guarded, pedigreed cultures in hisgarden, and also to breed the parent form, (Enothera La-marckiana, and see if he could observe the two forms abovementioned, or other mutants, arise from seed producedwithout crossing with any oth
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