Acta Phytotaxonomica et Geobotanica

Embryo sac development of D. japonica THUNB. and D. quinqueloba THUNB. has been studied. In both species, the ovules are anatropous, bitegmic and crassinucellate. The development of the embryo sac is of the Polygonum type. The writer wishes to express his thanks to Prof. Dr. Sadao SUGAYA of the Tohoku University for his kind guidance and also to Dr. Chugai KIMURA of the same university for his valuable advice throughout this investigation.

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1) About 250 species of the pteridophytes known in northern Thailand are arranged according to the distribution patterns and altitudinal occurrences. The Sino-Himalayan elements are predominant in the evergreen forests at higher elevation. Separated by the broad belt in Central Plain and Korat Plateau, Thailand is divided into two floristic regions which match well with the climatic division. No special floristic division is recognized for the pteridophytes of Thailand. 2) Doi Inthanon and Doi Chiang Dao are the mountains rich in the species of the pteridophytes. These two mountains are different from each other in edaphic and physiographic conditions. The pteridophytes of these two mountains are compared in details, and are concluded that their occurrences are generally speaking as the result of the ecological factors, especially under the influence of the climatic condition. 3) The habitats are peculiar within Thailand for several species. They are interpreted as the result of the ecological condition, especially of the presence of moisture.

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1. The vascular structure of the rhizome, stipe, and rachis was observed for 41 species of the athyrioid ferns (Athyrium, Diplazium, Cystopteris, and their relatives), for the problematic genera for their athyrioid affinity (Acystopteris, Gymnocarpium, Hypodematium, Matteuccia, Onoclea, Stenolepia, and Woodsia), and for the several groups to which those genera have been related. 2. The vascular structures are common to all the athyrioid ferns in strict sense except for a few specialized cases. Among the genera cited above, Acystopteris, Gymnocarpium, Hyodematium, Matteuccia, Onoclea, and Woodsia have quite the same vascular structure as that common to the athyrioid ferns, with an exception of the dorsiventral rhizome of Hypodematium. The vascular structure of Stenolepia is distinct from that of the athyrioid ferns, resembling that of the dryopteroid ferns. 3. Based on the vascular structure as well as the other taxonomic characters such as the trichome, sorus, and spore, it is concluded that Acystopteris, Gymnocarpium, Hypodematium, Matteuccia, Onoclea, and Woodsia are all belonging to the athyrioid group, and Stenolepia is better placed in the dryopteroid group.

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Observations are made on the development of embryo sac and embryo in Syneilesis palmata which is characterized by a single cotyledon. The ovule is anatropous. The embryo sac development follows the Polygonum type. The inner epidermis of integument forms the endothelium. At the early stage in the differentiation of cotyledon, the dicotyledon embryo is observed, but at the later stage, the intermediate embryo between dicotyledons and monocotyledons is found. The true nature of the single cotyledon in Syneilesis, however, has not yet been correctly identified.

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