Physiological and ecological studies on Digitaria plants. II : The rolls of the hulls of seeds to the germination of seeds of Digitaria sanguinalis Scop. var. ciliarsi Doell. I

1. Immature seeds, which had been lapsed 10～20 days after the flowering and were sown immediately after the removal from the parent plant, so as not to be acted by the natural drying process, germinated very rarely. However, by removing the hull (glume and palea) the germination of seeds was intensely accelerated (the germination percentage within 7 days at 35℃ was 90%). 2. When the yellow-riped seeds were stored in dry condition, the germination percentage of naked seeds. decreased gradually with the passage of time of storage, until the end of the thirty-day period after the lapse, when the value of the percentage became 8, within 7 days at 35℃ and afterwards the rate of germination gradually increased again with the lapse of the period in drying storage. The germination percentage of naked seeds, stored intactly 165 days in dry condition, was 68%, but this was restricted to the naked seeds, the intact seeds did not germinate. The seeds stored during 255 days, however, germinated 90% within 1 week at 35℃, regardless whether the hulls were removed or not. Thus the germinant power of the seeds was continued for about 200 days further, yet thereafter it was weakened. The seeds which had been kept in dry storage for 820 days after the harvest germinated only 30%, within 7 days at 35℃. 3. In order to be soaked throughly dormant seeds and the seeds, awakened from the sleep, were set on wet filter paper in a Petridish kept in an incubator of 35℃, during respectively 1 week for the former and 1 day for the latter, and then the hulls of seeds were carefully removed. Immediately afterwards half the number of these seeds (both dormant and awakened) were coated with paraffin. The naked dormant seeds were able to germinate but the coated dormant seeds did not germinate. The awakened seeds germinated well without regared to the presence or absence of the coat. 4. Though dormant sceds have covered perfectly with hull did not germinate, the removal of only O.6mm^2 of the hull from the center the outside surface of the seed enough permitted the germination. They showed nearly the same germination percentage as the thoroughly naked seeds. 5. Water-soluble substances extracted from the hull of seed were found scarcely to produce an inhibitory effect on germination of the naked seeds. 6. The result of a comparison of germination of seeds in water and on wet filter paper, indicated by the germinating percentage, within 7 days at 8～39℃ was as follows. a) On moistened filter paper in Petri-dishes: ……86% b) In the ordinary water which was stirred at times in oder to introduce oxygen in it. ……55% c) In the water without oxygen, which was abolished by boiling about 10 minutes: ……44% 7. From the experiments mentioned above it may be said that the hull suppressed the germinination by hindering the water inhibition of the seed, to such a limit that the germination was not permitted, and that the mechanical resistance and the preventing of oxygen permeation by the hull and the presence of some germination-inhibiting substances, rather, seem to bear no relation to the inhibition of germination. Seemingly the action of the hull was due chiefly to the palea. Note: For convenience, in this paper the term \u22seed\u22 is used to designate the caryopsis, and \u22hull\u22 the surrounding parts of caryopsis, namley the glume and palea.1. 開花後10～20日を経過したメヒシバの種子を採り播すると極めて僅かしか発芽しないが, 剥被すると大多数の種子が(35℃, 7日間で90%)発芽する. 2. 乾燥状態で黄熟種子を貯蔵すると, 剥被しても貯蔵日数の増すにつれて次第に発芽歩合が悪くなり, 貯蔵30日目には35℃, 7日間で8%発芽する. 共の後貯蔵日数の増すにつれて剥被種子の発芽歩合を増し, 165日目には35℃, 7日間で68%発芽するが, 剥被しない種子では発芽しない. しかし255日目には剥被の有無に関せず7日間, 35℃で90%発芽する様になる. そして此の状態が更に200日間位続くが, それ以上になると発芽歩合が落ちて, 貯蔵820日目には約30%しか発芽しなくなる. 3. ぺトリ皿の湿つた濾紙上に休眠中の種子及び休眠から覚めた種子を夫々播いて,35℃の定温器内に前者を1週間, 後者を1日置いて充分吸水せしめ, 後丁寧に共の外被を剥ぎ, 夫々の半数に外被の代りにパラフィンを塗布すると, 休眠種子では剥被しただけであるとよく発芽するが, 之にパラフィンを塗布すると発芽しなくなる. しかし休眠から醒めた種子では剥被のままでもパラフィン塗布のものでも共によく発芽する. 4. 休眠の種子では頴の中央部を小部分(0.6mm^2)を剥被しても, 全剥被に近い発芽歩合を示した. 5. 休眠種子の外被浸出液を剥被種子に加えても発芽抑制作用は殆んど認められない. 6. 水中に於ける発芽を湿潤濾紙Eの発芽に比較すると, 8～39℃の湿度に於て1週間の発芽歩合は次の通りであつた. a. ペトリ皿の濾紙上で86%, b. 酸素を溶存する水中で55%, c, 沸騰せしめて酸素を除去した水中で44%, 即ちメヒシバ種子では, 発芽にあまり多量の酸素を必要としない様である. 7. 以上の結果から外被の発芽抑制作用として, 外被の機械的圧力,呼吸作用に必要な酸素の滲透妨害, 発芽抑制物質の存在等はあまり考えられず, 寧ろ外被が水の浸透を妨げ, 種子をして発芽に必要な水分の最小限度以下の状態においているのではないかと思われる. 而して外被中護頴はゆるく内外頴に附着しているにすぎないので, 水分の透過を妨げているのは堅く頴果を包んでいる内外頴であろう. 備考, 本報文で言う種子とは実は頴果の事で, 外被とは頴果の周囲を包む護頴及び内外頴の総称である