著者

小林 義雄

出版者

日本植物分類学会

雑誌

植物分類,地理 (ISSN:00016799)

巻号頁・発行日

vol.33, pp.201-205, 1982

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Pollen tetrads of 36 species belonging to 26 genera of Japanese Orchids were observed in details. The results are as follows : 1) Confirmation of types of the pollen tetrads and morphological variation in each type of them ; The arrangement of the four young pollens in the tetrads is variable within 36 species observed, although they could be classified into six types such as tetrahedral, square, decussate, rhomboidal, T-shaped and linear ones. Throughout the species observed the pollens constituting a tetrad were intact, and aberrantly large or small ones in the aberrant tetrads were not recognized. 2) Estimation of mixing ratios in each type of the pollen tetrads ; All six types of the pollen tetrads were recognized in 30 among 36 species observed. The ratios in each type of the pollen tetrads are shown in Table 1. The decussate tetrads show the highest ratio, about 50% throughout the species except Habenaria radiata and Goodyera maximowicziana. Values of the ratios of each type decreased from the decussate tetrads in sequence of rhomboidal, tetrahedral, square, T-shaped and linear ones. Detailed observation on the ratios among the pollen tetrads in each type of Calanthe discolor showed that the ratios were similar through five individuals collected from three different localities ( Table 2). In Goodyera maximowicziana, higher ratios of the T-shaped tetrads and linear ones were observed in extremely slender basal part of the pollinium than those of T-shaped and linear ones of the other part of the pollinium. 3) Ontogenetical observation on each type of the pollen tetrads ; All tetrads observed were produced by simultaneous membrane formation. The course of the tetrad formation was proceeded in the pollen mother cells which were gathered into parenchymatously compact mass. The courses of the pollen tetrad formation of each type are schematically shown in Fig. 1 with photographs in Figs. 2 and 3. It seems that different types of the pollen tetrads are caused by the different forms of the pollen mother cells and by the difference of the direction of the two axes of the second nuclear divisions. It is concluded that the species in the Orchidaceae observed have several types of pollen tetrads within a single pollinium which all develop normally and that the types of pollen tetrads in this family would be determined by the direction of axis of cell division and the forms of pollen mother cells. The forms may be correlated to those of the pollinia and to the parenchymatously compact gathering of the pollen mother cells throughout the course of the tetrad formation.