The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . cessive years, that is to say the new species, in the formof radiating groups (Fig. 148). Each group denotes themutations in a single generation. The main stem contin-ues unchanged and successively produces the individualgroups. Together, however, they obviously belong to oneand the same period, inasmuch as each of them mainlyconsists of the same species and in approximately ecjualproportions. In order to compare this period with previous onesthe whole figure may be compressed to a single grou
The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . cessive years, that is to say the new species, in the formof radiating groups (Fig. 148). Each group denotes themutations in a single generation. The main stem contin-ues unchanged and successively produces the individualgroups. Together, however, they obviously belong to oneand the same period, inasmuch as each of them mainlyconsists of the same species and in approximately ecjualproportions. In order to compare this period with previous onesthe whole figure may be compressed to a single has been done in the upper part of Fig. 14^. Thelateral branches do not arise here from a single point, andthis is intended to indicate the fact that the figure em-braces a series of generations in which the variations wererepeated. As stated above, we will now assume that the ances-tors of our Oenothera have not always been our group must have a limit below, and nuist,so to speak, be borne by a stem without lateral brandies. 654 Geological Periods of Mutation. Oe^.La Fig. 148. Pedigree of Ocnotlicra Lamarckiana, exhibitingthe yearly origin of new species in my experimentalgarden in the years 1889-1899. g, O. gigas; a, O. albida;It, O. lata; 11, O. nanella; r, O. nihrincrvis; o, O. oblonga;s, O. sciufillans. The numbers preceding the letters arethose in which the species in question arose. The num-bers on the main stem show the extent of the yearly cul-tures. TJic Periodicity of Proyrcssiic Mutations. 655 XylonrCtuxum
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