The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . n. level of the ground (e. however, numerous exceptions. In tricotylous cultures, dicotylous individuals some-times become ternary later. Thus I possess a plant withternary whorls of Aesculus Hippocastanuni (now 13years old), which only had two cotyledons, and fromthe same crop a plant which was tricotylous but has sinceproduced leaves on the decussate plan only. In ]:)Otlispecimens the change in the disposition of the leaves Tricotyly and the Amuigciiicfit of Leaves. 371 toDk place before
The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . n. level of the ground (e. however, numerous exceptions. In tricotylous cultures, dicotylous individuals some-times become ternary later. Thus I possess a plant withternary whorls of Aesculus Hippocastanuni (now 13years old), which only had two cotyledons, and fromthe same crop a plant which was tricotylous but has sinceproduced leaves on the decussate plan only. In ]:)Otlispecimens the change in the disposition of the leaves Tricotyly and the Amuigciiicfit of Leaves. 371 toDk place before the cotyledons were dead. \\\ Dipsaeiissyl-iesfris tors its, a race which is usually ricli in lernar\-in(h\ iduals, these are almost without exception decussatein early youth. On the boundary between the 2- and 3-merous whorls2!/2-nierous ones not infrequently occur. I mean whorlswith one normal and one more or less deeply cleft degrees of cleavage (or symphysis) may occur. Inthe tricotylous races of Antirrhiniiui ma jus and Serophu-laria nodosa they are particularly abundant, and merge. Fig. yG. Mercnrialis annua. A, normal seedling; C, cotyl-edons, (i) the first, and (2) the second pair of leaves;B, a tricotylous seedling the first two leaves of whichstand opposite one another (1900). into the decussate arrangement in the first or second orin some later whorl. In the choice of seed-parents I havealways paid attention to this point, although it has onl}- asecondary effect upon the result. Further instances of cleftleaves in the transition from tricotyly to the later normalarrangement were afforded me by Dianthiis vespertina, Polygonum Fagopyrum, CoUinsia he-terophylla, Anagallis grandiflora and in large quantitiesby Fagus sylvatica (Fig. 75) as well as by many otherspecies. As the phenomenon is quite common whenmore extensive sowings are made and as, especially in 372 Tricot\lous Races. perennial plants, the transition from one mode of ar-rangement
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