シダモク(?)に関する観察及びその胚発生

In the previous paper the author reported some interesting characters of the sexual organs in Sargassum filicinum. Notwithstanding the strong resemblance between S. horneri and S. filicinum in the external shape excepting the difference in the vesicular shape remarked by W. H. Harvey, they are distinguishable in sexuality : the former is strictly dioecious while the latter monoecious and androgynous in the receptacle. In April 1955, he happened to obtain another alga with the ellipsoidal or somewhat ovato-fusiform vesicles. It may not be identified with a typical form of S. filicinum and also not undoubtedly with S. horneri. In this paper the author intends to report the results of observations on this alga especially on the sexual organs and the embryo-development, and also to try some comparison with those of S. horneri and S. filicinum. The material were collected with some bottom gill-nets, chiefly at Hutae, Amakusa Islands, Higo Province. The results are summarized as follows : 1) The alga in question bears strong resemblance to both S. horneri and S. filicinum in having the disco-fibrous root, the fine spinous processes on stem, the cylindrical receptacles, and the alternato-pinnatisected leaves, but is different by having the ellipsoidal vesicles (Fig. 1). 2) The alga seems to mature about in April to May in Amakusa Islands, so is it in S. horneri, but comparing with the latter the former may be later slightly. 3) The receptacles are androgynous ; besides male and female conceptacles the same receptacle harbours hermaphrodite ones (Fig. 2), but the number of hermaphrodite conceptacles is indeed less than the others in each receptacle. The male conceptacles are not more than the female's, and they are found in any part of the receptacle, not being confined in the basal part as in S. filicinum ; though they gather more in the basal part. In the hermaphrodite conceptacle the oogonia and the antheridial hairs are not intermingled, but occupy the side position to each other. 4) Discharge of oogonia takes place periodically, and the discharged portion advances acropetally in each receptacle, as is usual in many other members of the genus Sargassum. 5) Discharged oosphere is ellipsoidal measuring ca 265 x 205 p, which is surrounded by a thick layer of mucilaginous substance. Around the outer wall of the thick layer there is observed a girdle-like dissolved portion as is reported on S. horneri (Kunieda & Suto 1940) and S. filicinum (Sawada 1955). 6) The embryo-development takes the same course with S. horneri. The rhizoid cell is segmented into 8 radially arranged cells (" radial 8-cell type " by Inoh 1930), and yet those 8 rhizoids developed from the rhizoid cell another group of about 7 to 15 rhizoids are observed to begin growth.

1. 筆者はシダモクによく似た植物を天草に於て入手し, 観察を行つた結果,生殖器官並びに胚発生に関して若干の知見を得ることが出来た. 2. 外形はアカモク, シダモクと非常によく似ているが, 気胞が大概楕円形である点, これらとは少し異なる. が, その他では仮盤状の根, 刺状突起のある単条の茎, 葉, 冠葉等, 外観は殆ど異なるところはない. 3. 成熟期は, アカモクと略々同時期か或いは多少遅れるのではないかと思われる. 4. 生殖器托の外形は, アカモクの雌またシダモクのものと殆ど同じであるが, 生殖案の性状に関しては大いに異なつた点がある. 即ち雌雄の両生殖案の他に, hermaphrodite の生殖案も存在することは興味深く思われるが, 尚これら3種の生殖案は, 1生殖器托内に於てどの部分からも見出された. 又 hermaphrodite の生殖案にあつては, 雌雄はその案内に於て互に混生することなく, 案ロをはさんで両側に位置するものしか見られなかつた. 雄生殖案が生殖器托の基部の少部分に特に多く存在することは, シダモクに非常によく似た性質である. 5. 1生殖器托に於て, 卵の放出は基部から上部に向つて2～3回位に分けて行うものと思われる. 6. 放出卵は, 大きさが略々265×205μ の楕円形で, アカモク, シダモクのものと大体一致し, 膠質状物質に包まれて暫く生殖器托表に附著している. 精子の侵入位置としてはアカモク, シダモクと同様に, 蔵卵器中膜に帯状の膨潤部が観察された. 7. 胚発生の経過は, アカモクと同様な型をとると考えられる. 即ち仮根細胞は放射状に8箇に分割され, その後, 仮根細胞に起因しない仮根群が内側から伸び始めて, 合計10数本から20本前後の仮根が伸長を行う. 8. 仮根細胞に起因する仮根群が或る程度仲びた後に, その内側から別な仮根群が現れる例の多かつた事実は, 従来アカモクについて報含されていたものと必ずしも一致しない. しかし, アカモクに於ても今回の植物と同様な例を福岡市外の材料で観察することが出来たので, 胚発生に関してはアカモクに同じと考えても差支えないと思う.