The Female Conceptacle and Young Sporeling of the Four New Zealand Species of Carpophyllum
[Read by title before Otago Branch on July 14, 1953; received by Editor July 27, 1953.]
The four New Zealand species of Carpophyllum agree closely in details of conceptacle development, oogonium maturation and early segmentation of the sporeling. The oogonium contents are liberated in an eight nucleate condition and the maturation of the oosphere is completed after extrusion. A mucilaginous stalk formed from the oogonium wall retains the fertilised egg until the rhizoidal system of the sporeling is established.
The genus Carpophyllum is represented in New Zealand by four species—C. elongatum (Dickie) A. & E. S. Gepp, C. flexuosum (Esper) Grev., C. maschalo-carpum (Turn.) Grev. and C. plumosum (Ach. Rich.) J. Ag.—and the variety capillifolium J. Ag. of C. plumosum. The only descriptions of the reproductive structures of these species are those of Delf (1939) and Dawson (1940) who worked in England on preserved material sent from New Zealand. Owing to the restricted nature of their material these accounts are not complete and the present investigation is an attempt to fill in some of these gaps.
The C. elongatum was collected from Mokohinau Island, from Cape Brett and from Tapeka Point, Russell, but owing to difficulties involved in collecting from these exposed habitats, the account of this species is still incomplete. The remaining species were collected principally from Castor Bay, Auckland, supplemented by material from Russell. The fixative used throughout was Papenfuss's modification of Karpechenko fluid (Laing, 1941). Sections were cut at 8μ and stained with crystal violet or Heidenhain's iron alum haematoxylin for cytological details and with erythrosin or Delafield's haematoxylin for segmentations of the sporeling.
Early stages of conceptacle development have been described in C. elongatum and C. maschalocarpum by Delf and in C. flexuosum by Dawson and my observations show a similar sequence of divisions in C. plumosum (Text-figs. 1A–C).
In all four species only a few, relatively large oogonia develop in each conceptacle. At maturity they occupy almost the entire conceptacle cavity (Text-fig. 1D) and usually become angular as the result of mutual pressure. They are separated by groups of closely appressed moniliform hairs whose cells swell after the release of the oogonium contents and fill the spent conceptacles with pseudoparenchymatous tissue. Dawson found the average number of oogonia in a conceptacle to be nine in C. flexuosum. I find a similar number in C. plumosum and C. elongatum also, but in C. maschalocarpum usually only three or four reach maturity
and sometimes as few as two. In young conceptacles larger numbers of developing oogonia are seen, so possibly space considerations prevent their reaching maturity.
Oogonium Development and Maturation
The oogonia and the sterile hairs which separate them are at first indistinguishable, as both arise as papillae from the lining layer of the conceptacle. Soon the oogania can be distinguished by their more densely staining contents. The fully developed oogonia of C. elongatum, C. maschalocarpum and C. plumosum reach a length of about 142μ with a maximum diameter of 123μ in the first two species and 95μ in C. plumosum. After their liberation the oospheres become spherical with a diameter of up to 160μ in the two latter species, though C. plumosum tends to be rather smaller. A comparable measurement for extruded C. elongatum oospheres could not be obtained. The “almost mature oogonia” of C. elongatum
Text-Fig. 1.—A. B. C—Early stages of conceptacle development in C. plumosum var. capillifolium. A—Still within the apical groove and showing the formation of the tongue cell. B and C—Slightly order stages showing the concurrent development of the oogonia and the concrescent hairs. Scale = × 435.
D—Section of an almost mature conceptacle of C. maschalocarpum which contained 4 oogonia, showing the large oogonia and central tuft of hairs. Scale = × 285.
All outlines drawn with the aid of a camera lucida.
and C. maschalocarpum which Delf states to be “nearly spherical and have a diameter of 60–80μ.” must in fact have been little more than half grown. The oogonia of C. flexuosum are considerably larger, reaching a length of 210μ and width of 112μ before extrusion, and a diameter of 180μ after extrusion (cf. Dawson 178μ × 137μ).
Cytological maturation of the oosphere has hitherto been followed only in C. flexuosum where Dawson found the prophase of a large central nucleus and, after extrusion, an eight nucleate stage, but no intervening stages. In the present investigation, for several successive days mature female plants of all species except C. elongatum were marked on the shore and receptacles fixed at half-hourly intervals over the two hours for which they were accessible at low tide. In all cases a large central nucleus divided to give an eight nucleate stage, whilst the oosphere was still within the conceptacle. At first the eight nuclei were central in position (Text-fig. 2D), but soon migrated to the periphery (Text-fig. 3A). In this condition, with eight peripheral nuclei of equal size, the oogonium contents— “oocyte” (Mitchell, 1941)—were liberated (Text-fig. 3B). Seven of the nuclei then degenerated, appearing smaller, flattened and densely staining during the process (Text-fig. 3C). In no case was there any evidence of degeneration of the supernumerary nuclei before extrusion; it was not possible to determine whether this degeneration took place before fertilisation or after as in Sargassum horneri
Text-Fig. 2.—A, B, C, D—Stages in the enlargement and maturation of the oogonium of C. plumosum var. capillifolium whilst still within the conceptacle. AA-CC—The nuclei from the oogonia to a higher magnification. EE—Nucleus from an oogonium similar to C, but with the chromatin more deeply staining. FF—A nucleus with two nucleoli. Similar stages have been found in C. flexuosum and C. maschalocarpum.
All outlines drawn with the aid of a camera lucida. Scale: A-D = × 200; AA-FF = × 900.
Text-Fig. 3.—Oogonia of C. maschalocarpum showing the final stages of maturation. A—An eight nucleate oogonium still within the conceptacle as in 2D, but with the eight nuclei peripherally arranged. Built up from 12 consecutive sections. B—An eight nucleate oogonium after extrusion, but before degeneration of the supernumerary nuclei. Built up from 16 consecutive sections. C—An eight nucleate oogonium after extrusion, but with seven nuclei degenerating, and with the one functional nucleus in a peripheral position. Built up from 24 consecutive sections. The numbers indicate the level of the section in which that nucleus appeared. Scale = × 275.
and S. tortile, or whether fertilisation took place whilst the nucleus was in a peripheral position or whether it first migrated to the centre.
No four-nucleate oogonia were found, nor any stages in nuclear division. This may be due to the limited time range over which fixations were made —i.e., from approximately 8.30 a.m. until 11.30 a.m.—as Abe (1938) found that nuclear division in Sargassum tortile commenced during the afternoon and was completed by the following morning when extrusion took place.
Extrusion and Embryology
In all four species, the liberated oogonium contents are not released free into the sea but remain attached to the receptacle by a firm, mucilaginous stalk formed from the oogonium wall. In this position fertilisation takes place and sporeling development commences.
Dawson described sporelings with a tuft of sixteen rhizoids in C. flexuosum, and Delf described well developed sporelings but was unable to assign them to a species. In the present investigation sporeling development was followed from attached sporelings in the three species in which they were found—that is, in all except C. elongatum. The first median wall (Text-fig. 4A) dividing the sporeling into two multinucleate portions was seen only in C. plumosum, but the following stages were found in all three species. A protuberance next developed at one end and was cut off to form a relatively large, densely staining, multinucleate rhizoid initial (Text-fig. 4B), which soon divided longitudinally (Text-fig. 4C) to produce a basal tuft of sixteen rhizoids (Text-fig. 4J). Meanwhile subdivisions in the body of the sporeling had resulted in the formation of a small-celled surface layer enclosing a central region (Text-fig. 4F). In the most advanced of the attached sporelings, transverse sections showed about 16 peripheral cells surrounding 8 central ones (Text-figs. 4G and L), obviously the result of a regular sequence of cell division (Text-figs. 4G, H, K) which had consisted of two vertical walls at
right angles, followed, in each quadrant so formed, by a wall approximately parallel to one of the first formed walls. Each portion so formed then gave rise to an inner and an outer cell by a fairly regular sequence of walls. There was no constant orientation of the longitudinal axis in relation to the receptacle, as can be seen by comparing the position of the attaching stalks in Text-figs. 4B, D and F.
Text-Fig. 4.—Sections and surface views of young sporelings. A, B, C, K and L. C. plumosum var. capillifolium. D—C. flexuosum. E, F, G, H, J—C. maschalocarpum. Except for stage A comparable stages were seen in all three species in which sporelings were found. A, B, C, D and F are median longitudinal sections. E—A surface view of a week-old living sporeling. G, H, J—Transverse sections of the same sporeling of C. maschalocarpum at different levels. K and L—Transverse sections of two sporelings of C. plumosum of slightly different ages showing the regular sequence of wall formation. Outlines drawn with the aid of a camera lucida. Scale = × 140.
By this stage the rhizoidal system was well established and the sporeling became detached. It was not possible to judge how long the sporelings remained attached in nature, but in all three species followed, attached sporelings were found which were comparable in size and differentiation with some in cultures of C. maschalocarpum a week after fertilisation.
In the formation of a tongue cell cut off by a curved wall, the species of Carpophyllum investigated resemble other members of the Sargassaceae, of which details are known.
Late maturation of the oosphere is characteristic of those Sargassaceae in which the oosphere is retained, and the degeneration in situ of the supernumerary nuclei is also in agreement with other members of the Sargassaceae and in contrast to the condition in the Cystoseiraceae where they are extruded from the cytoplasm.
The sequence of segmentation in the sporeling resembles that in Coccophora langsdorfii (Tahara, 1928), Turbinaria fusiformis and T. thunbergii (Tahara, 1929) and in Cystophyllum sisymbrioides (Okabe, 1929), but differs from that usual in Sargassum where the third vertical wall is radial, dividing the body of the sporeling into octants, a feature considered by Tahara (1928) to be of systematic value.
The production of a tuft of primary rhizoids is also a feature of the family Sargassaceae. Inoh (1930) attempted to correlate the number of primary rhizoids with the size of the oosphere in Sargassum. In all the species of Carpophyllum investigated the egg is considerably smaller than in any of the Sargassum species with the same number of rhizoids (16), but is more comparable with those producing only eight.
Part of this investigation was carried out during the tenure of a Research Fund Fellowship of the University of New Zealand.
Abe, K., 1938. Über die Befruchtung und ihre folgende erste Kernteilung bei Sargassum. Sci. Repr. Tohoku Imp. Univ. Fourth Series. Sendai. Japan, 13. 253
Dawson, A. E. E., 1940. Studies in the Fucales of New Zealand II. Observations on the Female Frond of Carpophyllum flexuosum (Esper) Grev. New Phytol., 39. 283.
Delf, E. M., 1939. Studies in the Fucales of New Zealand I. The genus Carpophyllum Grev. J. Bot., 77. 129.
Inoh., S., 1930. Embryological Studies on Sargassum. Sci. Repr. Tohuku Imp. Univ. Fourth Series Sendai. Japan, 5. 423.
Laing, E. M., 1941. A Note on Bifurcaria laevigata (Kütz) Delf et Mitch J. Bot., 79. 145.
Mitchell, M., 1941. Studies in the Fucales of New Zealand III. Some Investigations on Xiphophora chondrophylla. J. Bot., 79. 49.
Okabe, S., 1929. Rhizoidenentwicklung im Embryo von Cystophyllum. Sci. Repr. Tohoku Imp. Univ. Fourth Series. Sendai. Japan, 4. 591.
Tahara, M., 1928. Contributions to the Morphology of Coccophora langsdorfii (Turn) Grev. Ibid., 3. 727.
— 1929. Rhizoid formation in the Embryo of Turbinaria (?) fusiformis Yendo and Sargassum Thunbergii O. Kuntze. Ibid., 4. 1.