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Spore Germination and Vegetative Stages of the Gametophytes of Hymenophyllum and Trichomanes

1940; University of Chicago Press; Volume: 101; Issue: 4 Linguagem: Inglês

10.1086/334914

1940-1205

Alma G. Stokey,

Lichen and fungal ecology

1. Germination stages are given for seven species of Hymenophyllum: H. acanthoides, H. blumeanum, H. fuscum, H. holochilum, H. junghuhnii, H. kurzii, and H. javanicum. The spores germinated while still in the sporangium with the formation of a cross wall followed by a second wall meeting the first in the center of the spore. The walls separating the three cells lie under the tripartite ridges of the spore coat. Occasionally the second wall is delayed until after discharge of the spores, or it may be suppressed. 2. After rupture of the spore coat the young gametophyte assumes the form of a triangular cushion, with the three tips growing in the direction of the longitudinal axes of the valves of the spore coat. 3. Secondary walls arise in sequence, cutting off a small cell from each tip. Development is usually symmetrical up to the 6-celled stage, but the next stages are more variable. In H. acanthoides, H. blumeanum, H. holochilum, and H. kurzii growth of one tip results in a plate; growth of the other two is checked sooner or later by rhizoid formation. The prothallus develops as a branching ribbon-like structure, which at one year may have branches 9-12 mm. long. In H. fuscum and H. javanicum growth is much slower; the later growth is filamentous in form with occasional longitudinal divisions but without plate formation. 4. Rhizoid development is belated in Hymenophyllum; the first rhizoid usually appears when there are six to eight cells in the gametophyte. The rhizoids have heavy brown walls; they may arise from any cell of a filament, but arise only from marginal cells of the ribbon-like thallus. Branching rhizoids are common, particularly near the base of the gametophyte; frequently two rhizoids grow from one cell. 5. The gametophytes of H. holochilum and H. kurzii reached maturity in twenty months, bearing both antheridia and archegonia. H. blumeanum did not produce archegonia until nearly four years old. 6. Germination in Trichomanes nitidulum is like that in Hymenophyllum, with the spore dividing into three cells. Subsequent stages were less regular than in Hymenophyllum and there was no plate formation. The gametophytes remained filamentous, with longitudinal divisions in a few cells or sections of a filament. 7. In T. auriculatum and T. bilabiatum, after rupture of the spore coat and before any divisions have occurred, the spore assumes the form of a triangular cushion. The first walls cut off the three tips, leaving an undivided central cell. If growth is slow, as in the case of spores which fall into the indusium and germinate there, the 4-celled stage is symmetrical; but if conditions for growth are favorable, the form is more irregular, particularly in T. auriculatum in which the first tip cut off usually forms a rhizoid in which growth is relatively rapid. The wall cutting off the third tip is frequently delayed, especially in T. auriculatum. 8. Germination in T. maximum may conform to the 4-celled type, but it is usually less regular. There is a tendency toward suppression of one of the tips, or sometimes merely a delay in wall formation in one tip. The gametophyte may then develop as a straight or a lopsided filament, rather than as a triradiate structure. Growth and development in T. maximum are extremely slow. 9. The mature gametophytes of T. auriculatum and T. bilabiatum are of the branching filamentous type without longitudinal divisions, forming a "turf" in compact cultures. They attained maturity, producing antheridia and archegonia, in nine to ten months. The gametophyte of T. maximum, although developing much more slowly, was similar in form and habit. Antheridia were formed on gametophytes one year old. 10. A variation from the usual type of germination in Hymenophyllum was found occasionally in several species. It suggests how the two types of germination in the family may be related. Reasons are given for looking upon the Hymenophyllum type as the older. Gametophytes of Hymenophyllum are found occasionally in which only one primary wall is formed at germination; the second is suppressed. The 4-celled type found in most species of Trichomanes might have arisen from the type found in Hymenophyllum (and a few species of Trichomanes) by the suppression of both of the primary walls, leaving the central part of the spore undivided. In the latter type of germination the first walls to appear in the spore correspond to the secondary walls which appear in the tips of the triangular gametophyte of Hymenophyllum.