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Volume 68, 1938-39
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Discussion.

(a) Antheridium. The development of the antheridium is very similar to that described for other Mosses and differs only in slight details. The first of these is the very early setting apart of the

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Fig. 1.—Gametophore of C. bulbosum ventral view. Nat. size. Fig. 2.—Diagram of L.S. main stem showing lateral sex branches, sex organs omitted; X 30. Fig. 3.—L.S. archegonial branch; large archegonium shows a young embryo; X 70. Figs. 4–9.—Development of antheridium as seen in L.S. before advent of periclinal division; X 570. Figs. 10–11.—Ditto, showing advent of periclinal division; X 570. Figs. 12–18.—Advent of periclinal division as seen in transverse section; X 570.

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Fig. 19.—L.S. antheridium; fertile tissue undivided;X 570. Fig. 20.—Ditto, fertile tissue sub-divided; p.: paraphyses; st.: stalk of mature antheridium; X 290. Fig. 21.—Ditto, showing all nuclei in one segment dividing; X 570. Fig. 22.—L.S. nearly mature antheridium; X 150. Fig. 23.—Ditto of apex to show apical cell still intact; X 570. Figs. 24–28.—Development of archegonium from “2-sided” apical cell; X 700. Figs. 29–30.—Formation of “3-sided” apical cell; X 700. Fig. 31.—Division of apical cell; t: terminal cell; i: inner cell; X 700. Fig. 32.—T.S. “2-sided” apical cell; X 350. Fig. 33.—Ditto, “3-sided” apical cell; X 350. Fig. 34.—T.S. of neck; X 350.

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Fig. 35.—L.S. archegonium; inner cell divided to give primary ventral cell (1) and primary canal initial (p); X 700. Fig. 36.—Ditto, showing primary ventral cell (p) and two neck canal cells X 700. Fig. 37.—Ditto showing intercalary division; primary ventral cell (p) still undivided X 350. Fig. 38.—L.S. older archegonium showing division in neck canal wall, and apical cell: X 350. Fig. 39.—L.S. apex mature archegonium with apical cell adding a segment to the canal row; X 700. Fig. 40.—L.S. mature archegonium; X 175. Fig. 41.—L.S. embryo in venter showing first wall; X 300. Fig. 42.—L.S. embryo in 3-celled stage; X 300. Figs. 43–45.—L.S. older embryos; X 150. Figs. 46 a–k.—Serial T.S. through one embryo from apex; en: endothecium. a: amphithecium; X 605. Fig. 47.—T.S. showing variation in formation of endothecium; X 605.

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Fig. 48.—L.S. apex of sporogonium; en: endothecium; X 300. Fig. 49.—L.S. complete sporogonium; X 75. Figs. 50–59.—Transverse sections of sporogonia showing development of endothecium (en) and amphithecium (a); X 400. Figs. 60–64.—division of amphithecium and endothecium; o.sp.s.: outer spore sac, p: peripheral cells; c: central cells; X 400.

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Figs. 65–67.—Diagrams to show development of sporogonium, calyptra, etc.; c: calyptra. vg.: vaginula. Figs. 65 and 66.—X 50. Fig. 67.—X 35. Fig. 68.—L.S. very young capsule; a.s: air space, c: calyptra, s: seta. f: foot, vg: vaginula; X 37. Fig. 69.—L.S. upper portion of young capsule (cf. Fig. 68). not perfectly median at apex; X 150.

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Fig. 70.—L.S. immature capsule; a.s.: air space, sp: sporogonial tissue; X 50. Fig. 71.—T.S. foot, and surrounding gametophytic tissue. N.B., dense cytoplasm; X 172. Figs. 72–74.—Division of sporogenous tissue; o.sp.s.: outer spore sac; X 300. Fig. 75.—L.S. portion of peristome showing one tooth; X 150. Fig. 76.—L.S. apex of capsule showing apical cell; X 300.

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Figs. 77–79.—T.S. young capsule showing development of air space (a.s.): o.sp.s.: outer spore sac, 1: inner wall of capsule, sp.: sporogenous tissue; X 300. Fig. 80.—T.S. seta with conducting strand; X200. Fig. 81.—L.S. upper portion of immature capsule; a.: annulus, a.s.: air space, sp.: sporogenous tissue; X 100.

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Fig. 82.—T.S. immature capsule; a.s.: air space, c.: columella; sp.: sporogenous tissue; X 150. Fig. 83.—Ditto, sporogenous tissue dividing; X 150. Fig. 84.—L.S. spore sac with spore “tetrads”: o.sp.s.: outer spore sac; tl.: “tapetal” layer; X 300. Fig. 85.—T.S. portion of mature capsule; s.: spores, a.s.: air space, tl.: “tapetal” layer; X 150. Fig. 86.—T.S. peristome before operculum is shed; t: tooth; X 150. Fig. 87.—Ditto, near base of peristome; X 150. Fig. 88.—L.S. mature capsule, operculum shed; a.s.: air space, c.: columella; p.: spore mass. o.sp.s.: outer spore sac reduced to a membrane: X 30.

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two-sided apical cells, before any pedicel is apparent. (This also occurs in Mnium, Holferty 21.) The segmentation of the antheridium to cut off central spermatogenous cells is somewhat different from that described by Goebel (17, p. 13); and Ruhland (29, p. 66). The succession of walls given by them is shown in Diagram II. In the species described by these authors the walls b–b both meet the primary wall a–a at the same point. Similarly with the third series c–c. In Cyathophorum (see Diagram I) the walls b–b are approximately parallel and meet the primary wall towards opposite ends. In Funaria hygrometrica (Campbell 13) the succession of walls corresponds to that given for Cyathophorum (Diagram I). The account of the apical cell has already been given.

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Diagram II.

(b)Archegonium. As already noted, there appears to be some confusion as to the exact manner in which the archegonium grows and forms the axial row. Campbell, Goebel. Holferty and others distinguish the archegonium of the Musci from that of the Hepaticae by the fact that the cover cell is active in the former, adding both to the cells of the neck and to the axial row. It thus seems fairly clear that in Musci the archegonium grows in length as a result of segmentation by the three-sided apical cell. How far this apical cell or cover cell is responsible for the cells of the canal row is however not so clear.

According to Campbell (13) in Funaria hygrometrica the terminal mother cell of the young archegonium divides transversely, giving rise to an upper cell, corresponding to the cover cell of the Liverworts, and an inner cell which produces the primary neck canal cell, the egg and the ventral cell. The cover cell functions as an apical cell cutting off lateral segments which give rise to the outer cells of the neck, and also segments parallel to the base to form the cells of the neck canal. Thus in this account all the neck canal cells arise from the apical cell, with the exception of the primary neck canal cell. This appears to persist as the lowest of the cells in the canal row lying immediately above the ventral canal cell. Campbell (loc. cit.) states definitely that “the canal cells so far as could be determined do not divide after they are first formed.” In Cyathophorum however this is evidently not the case.

G. M. Holferty (21) for Mnium cuspidatum gives the same general sequence of events except that he holds that the primary neck canal cell undergoes intercalary divisions. The cells cut off from the apical may also undergo intercalary division. Thus here the uppermost cells of the neck canal series are different in origin from those towards the base.

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G. S. Bryan (11) in his work on Sphagnum subsecundum finds no evidence that any cells of the canal row are derived from the apical cell—the whole series being due entirely to intercalary divisions of the primary neck canal cell. Thus Sphagnum appears to be one of the Musci in which the archegonium shows distinct Hepatic characters.

Gayet (16) holds that growth of the archegonium in both Musci and Hepaticeae is terminal, but that the apical cell does not add to the canal row. As noted by Bryan (11), this view appears to be rather a contradiction.

The present investigation supports the view advanced by Holferty (21) viz., that the neck canal cells are derived in part from the apical cell. Intercalary divisions definitely do occur, adding further to the length of the neck.

(c) Sporogonium. As already noted, the early stages in development of the sporogonium of Cyathophorum differ from those in Andreaea and Funaria. The very elongated embryo resulting from a number of transverse divisions offers some analogy with the embryos of Sphagnum (Campbell 13) and even of Fossombronia (Humphrey 22). Of course such a comparison is very superficial and applies only to the first few divisions. Once the two-sided apical cell is formed this similarity ceases and development follows the usual course for the true mosses. In the development of the sex organs and the sporogonium as given above, it is seen that there are no fundamental differences between Cyathophorum and such other mosses as have been described. There are, however, differences in detail, as is only to be expected in such a large group.

As regards the embedding of the lower part of the seta in the tissue of the gametophore, Vaizey (31) for Polytrichum notes “that it is apparently effected by the cells of the young calyptra becoming hard and thick-walled before it is separated from the vaginula.” He goes on to explain that with further growth the apex of the young sporogonium is unable to push past the calyptra, and hence “the lower apex is forced down into the stem of the oophyte through the softer to the harder tissues, when the pressure on the ealyptra becomes so great that it is torn away from the vaginula.” Actually in Cyathophorum the apex and the whole upper part of the young sporogonium do not touch the calyptra at all (Fig. 49). The actual portion of the embryo which appears to force off the calyptra is the “swelling” which later gives rise to the capsule, and especially the peculiar “collar” of tissue already referred to. However, neither the “swelling” nor the “collar” develop until the embryo is some size, yet in spite of this fact its lower extremity has already penetrated practically as far as it ever does. Although this is partially explained by the secondary growth of the venter, it seems that some process of digestion by the young embryo is responsible for the appearance usually attributed to the “growing down” of the seta at a later stage.

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