二三のアヤメ属植物における単面葉の背腹構造

Abstract

In all Iris species with unifacial leaves the rhizome lies in the soil horizontally and is distinctly dorsiventral. In most of them, the foliage shoots with equitant and isobilateral leaves which stand erect, both leaf surfaces being exposed equally to light and gravity. However, some species, for instance, Iris gracilipes A. Gray, Iris tectorum Maxim., etc. have plagiotropic shoots which do not show any anatomical unequality of the surfaces of their leaves.In the species described in the present report a structural dorsiventrality was found. In ris formosana the seedling has, except for the first 1 or 2, dorsiventral leaves. The dorsiventrality can be inverted by changing their direction in relation to gravity, as in Iris japonica. In Iris uniflora and Iris Rossii the seedling is not dorsiventral but the lateral shoots are distinctly so. Once established, this dorsiventrality cannot be inverted by changing the direction in respect to external factors. The growing point seems to be determined dorsiventrally and it gives rise to leaves with unequal surfaces. In this case also gravity seems to have the determining rôle. In the mode of induction Iris Wilsoni and Iris Bulleyana seem to belong to the stable type.It is noteworthy that all the above species are members of Asiatic flora. They Cbelong to the section Apogon except Iris japonica and Iris formosana, which are representatives of the section Evansia. The taxonomic or systematic significance of leaf dorsiventrality cannot be evaluated until more Iris species are thoroughly examined. In literature the indications are that many have leaves with unequal surfaces.* The causal sequence of aitiogenous induction of dorsiventral differentiation of the leaves is yet obscure. The unequal distribution of food materials and some determining hormones may probably be the factors which cause the unequal differentiation, as can be assumed from the eccentric growth in the thickness of the inclined trunks or lateral branches in many plants (14, 15). For the materials used in the present study we are indebted to Dr. M. Reed, Brooklyn Botanic Garden, U.S.A., Dr. Yu, Ching-jang, Dr. Shoichi Tanaka, Mr. Ryuhon Saito and Mr. Taketo Mizoguchi. We wish to express to all the above mentioned persons our sincere thanks for kindly supplying the rare plant materials.