ヒメジョオンの群の多型性について(第2報) : 生活史におけるロゼットの地位

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In a previous report of this study (Miscellaneous Reports of the Research Institute for Natural Resources, Nos. 17-18, pp. 136-144, Nov. 1950), the authors described seven taxonomic subdivisions discovered in the cathegory covering Erigeron annuus Pers. and E. strigosus Muhl. These subdivisions were provisionally named as follows : brevipes, strigosus, pseudoannuus, villosus, viridis, annuus and macranthus. Their discrimination was based on the external features of flowering shoots, heads and leaves in the summer rosette. Leaves of the winter rosette were not used for discrimination. The summer rosette develops in warm season and its leaves have long ascending petioles and wide leaf-blades. The winter rosette develops in cold season, and its leaves are adpressed to the ground surface, having long decurrent or decurrently lobulated leaf-blades with short petioles. In the first part of this paper, situation of two kinds of rosettes in the life history of the seven subdivisions was discussed. In a summer flowering shoot of the subdivision viridis, for example, a series of leaves is arranged on a stem changing successively in their formes from the base upwards to the top of the stem. Representative leaftypes picked out at intervals from this series are shown in fig.1, and are described as follows ; type-0 ; long petiolated-type, type-1 ; decurrent or decurrently lobulated-type, type-2 ; widely petiolated-type, type-3 ; sessile-type, type-4 ; bracteate-type. Occurreces of successive changes noted in the subdivision viridis are also observed in the remaining six subdivisions. As the features of the changes are alike in the same subdivision, but are more or less different in the different subdivisions, these differences can be taken as good taxonomic characters for distinguishing the seven subdivisions named above. Naturally, the changes of leaf-forms continue from the stem of the rosette on to the flowering stem developed from it. In cold season, each of seven subdivisions is represented only by the winter rosette, where leaves of type-0, 2, 3 and 4 are suppressed while those of type-1 are well developed. Hence, leaves belonging type-1 are predominant in winter rosettes. At the beginning of warm season, rosettes already matured develop the flowering stems, and leaves of type-2, 3 and 4 develop successively succeeding the type-1 leaves of winter rosettes. Rosettes immature at that time later transform into summer rosettes, which consist only of the type-0 leaves, until they grow large enough to develop the flowering stems, on which leaves of type-2, 3 and 4 are well developed, while those of type-1 are but poorly represented or often suppressed. These facts show that the features of the successive changes are differently represented according to the different seasonal environments. The element of seasonal environments, however, which influences the successive changes is considered to be chiefly the temperature, because a trace of the photoperiodicity is not observed in this group of Erigeron. Lastly, the descriptions of winter rosettes were dealt with. It was made clear by the authors that winter rosettes have enough taxonomic value for the discrimination of the seven subdivisions (cf. fig.2). Photographs of winter rosettes in late autumn were shown in fig.3. In such winter rosettes leaves of type-0, the typical summer forms, are seen still surviving.

ヒメジョオンの群の多型性について(第2報) : 生活史におけるロゼットの地位

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