ON THE RELEASE OF SPERMS IN ATRICHUM

An antheridium of Atrichum contracts when it opens. This contraction rapidly ejects much of the mass of sperms because a fluid present in the base of the antheridial chamber acts as an hydraulic ram. The residue of sperms is slowly extruded as the same fluid takes up water. Photographs allow the construction of time courses that directly demonstrate the existence of two phases (rapid vs. slow) in sperm release. Antheridia open as quickly in 1 m sucrose as they do in water. Molar sucrose allows only the rapid phase of sperm release, caused by the contraction of the jacket, and the antheridia remain only partly emptied. This behavior in sucrose solution provides a convenient test for similarities among antheridia. The mechanism of sperm release that occurs in Atrichum occurs in Polytrichum and Mnium as well.     

THE LIFE HISTORY OF CALLITHAMNION BYSSOIDES IN CULTURE

The life history of Callithamnion byssoides Arnott ex Harv. in Hook. has been shown to comprise a regular sequence of gametophytic, carposporophytic, and tetrasporophytic phases in unialgal culture using supplemented seawater media. Tetraspore germlings gave rise to gametophytes bearing either antheridia or carpogonia in 13 days. Fertilization, carposporophyte development, and carpospore release took place within 5 days. Carpospore germlings produced mature tetrasporophytes in 13 days. The life history thus required approximately 1 month for completion. No deviations from this pattern were observed.     

UNUSUAL DARK-GROWTH AND ANTHERIDIAL DIFFERENTIATION IN SOME GAMETOPHYTES OF THE FERN ONOCLEA SENSIBILIS

A fertile frond of O. sensibitis was found which yielded spores with unusual growth characteristics. About 25% of the gametophytes derived from the spores were able to undergo 2-dimensional development in darkness, in contrast to normal plants which are filamentous in darkness. When the aberrant spores were cultured in darkness under conditions of reduced ethylene concentration, the proportion of 2-dimensional plants rose to 75%, and, moreover, up to 50% of the gametophytes produced antheridia within 2 weeks. Under comparable conditions normal gametophytes produced no antheridia. The medium from antheridial cultures of the aberrant spores failed to induce the formation of antheridia in other plants.     

THE RELEASE MECHANISM AND LOCOMOTOR BEHAVIOR OF EQUISETUM SPERM

When antheridia of gametophytes of Equisetum hyemale L. are placed in water, only spermatid cells are released. These spermatid cells have from 6–12 fibrils radiating from 2–4 loci on the cell wall. One sperm is released from each spermatid cell. With high speed cinemicrography, it can be shown that sperm flagella beat three dimensionally with a continuous, traveling helical wave. A flagellar beat cycle is completed every 0.03 sec. In water the sperm swim rapidly at a rate of 300 μ per sec and traverse a helical path of long wavelength and shallow amplitude. Calcium is essential for normal locomotor behavior. When calcium is chelated by ethylenediaminetetraacetate (EDTA), the sperm spin in place. All other monovalent and divalent ionic solutions tested cause the sperm to swim abnormally. Monovalent ionic solutions prevent the drastic change in sperm mobility patterns resulting from chelation by EDTA.     

THE LIFE HISTORY OF POLYSIPHONIA DENUDATA (DILLWYN) KÜTZING IN CULTURE1

The sequence of somatic phases in the life history of the red alga Polysiphonia denudata has been determined in unialgal culture, using supplemented seawater media. Tetraspores gave rise to sexual plants bearing either antheridia or carpogonia in 50 days. Fertilization occurred within 1 week and the fertilized carpogonium developed to produce the mature carposporophytic phase in approximately another week. Carpospores formed by the carposporophyte germinated to produce the tetrasporangium-bearing phase, which released tetraspores in 44 days, thus completing the life history in 3^1/2% months. No deviations from this pattern have so far been observed.     

DIVISION OF THE GENERATIVE CELL AND LATE DEVELOPMENT IN THE MALE GAMETOPHYTE OF GINKGO BILOBA

Division of the generative cell in the male gametophyte of Ginkgo biloba to yield the sterile cell and spermatogenous cell was examined in vivo and in vitro. Evidence is presented in support of a new interpretation of development in which the sterile cell and spermatogenous cell arise from an unusual anticlinal ringlike division of the generative cell. This type of cell division is only known to occur during antheridial development in leptosporangiate ferns and stomatal development among certain ferns in the Schizaeaceae and Polypodiaceae. The strong similarities in development and cell arrangement within the male gametophytes of cycads and Ginkgo suggest that division of the generative cell in cycads may be the same as in Ginkgo. Although the ringlike (conically annular) divisions in the antheridia of leptosporangiate ferns and the male gametophytes of Ginkgo (and probably cycads) are remarkably similar and result in the production of a central spermatogenous cell, it is conjectural as to whether these patterns represent a striking convergence or evolutionary homology.     

A BIOSYSTEMATIC STUDY OF THE POLYGONUM HYDROPIPEROIDES (POLYGONACEAE) COMPLEX

The Polygonum hydropiperoides complex includes P. hydropiperoides Michx., P. opelousanum Riddell ex Small, P. setaceum Baldwin ex Ell., and P. hisutum Walter. Studies of morphology, cytology, and crossing compatibility were conducted with specimens from North Carolina, South Carolina, Georgia, and Florida. A multivariate cluster analysis using 212 specimens and 34 characters indicated that P. hirsutum and P. setaceum are each morphologically distinct while P. hydropiperoides and P. opelousanum are morphologically indistinct from one another. The chromosome counts of 2n = 20 for P. setaceum and P. hirsutum, and 2n = 40 for P. hydropiperoides and P. opelousanum are the first reported for the respective species. Experimental hybridizations produced the fertile hybrids P. hydropiperoides x opelousanum and P. setaceum × hirsutum. Results of these studies and population structure, habitat, and pollination studies suggest that P. hydropiperoides, P. setaceum, and P. hirsutum are each distinct species while P. opelousanum is indistinct and should be merged with P. hydropiperoides.     

How do sexual expression,reproductive phenology and reproductive success relate to sexual systems in Fissidens Hedw. (Fissidentaceae)? A case study comparing two different sexual systems in mosses

• Reproductive performance is known to differ between co‐sexual and non‐co‐sexual species. Thus, our aim was to determine whether: (i) the distance between sex structures is negatively associated with sex expression; (ii) male gametangia take longer to mature in rhizautoicous species than in gonioautoicous species; and (iii) the gonioautoicous sexual system has greater reproductive success (i.e. percentage of ramets with sporophyte) than the rhizautoicous sexual system.
• One population each of the mosses Fissidens scariosus and F. submarginatus, rhizautoicous and gonioautoicous, respectively, in a remnant of Atlantic Forest in Brazil were sampled monthly from September 2016 until August 2017. The number and phenophases of antheridia, archegonia and sporophytes were analysed for each species. Sexual expression and reproductive success were calculated, and reproductive phenology compared across environmental variables.
• As expected, sexual expression was significantly higher for the gonioautoicous species, which produced antheridia throughout the year and archegonia over many months, while gametangia production by the rhizautoicous species occurred only during the rainy season. Mean number of gametangia per perigonium and perichaetium were slightly higher for the rhizautoicous species (6.84 antheridia; 11.38 archegonia) than for the gonioautoicous species (4.39; 7.62). Gametangia and sporophyte production in the rhizautoicous species were markedly seasonal compared to that of the gonioautoicous species, although reproductive success did not differ.
• Therefore, we infer that the rhizautoicy (i.e. a functional dioicy) promotes lower expression of gametangia compared to gonioautoicy but is more efficient and so obtains the same reproductive success.

     

SEXUAL DEVELOPMENT OF ONOCLEA SENSIBILIS ON AGAR AND SOIL MEDIA WITHOUT THE ADDITION OF ANTHERIDIOGEN

Onoclea sensibilis gametophytes grown on agar, unsterilized soil or ashed soil without the addition of antheridiogen developed antheridia after the notch meristem was formed. There was a linear increase in maleness through time on all three media. Antheridial production on agar was delayed nearly 3 wk. Agar had a significantly higher proportion of females than ashed soil or unsterilized soil. It was concluded that agar is an inappropriate medium for experiments on the mechanism of sexual development in Onoclea gametophytes.     

A STUDY OF THE SPERMATOZOIDS OF DICHOTOMOSIPHON TUBEROSUS (CHLOROPHYCEAE)1

Spermatozoids of the siphonous green alga Dichotomosiphon tuberosus (A. Br.) Ernst are specialized gametes which differ in many respects from other green algal motile cells, but whose microanatomy nevertheless indicates its chlorophycean affinities. Each cell is anteriorly biflagellate and contains an irregularly shaped nucleus attached to the flagellar bases by a complex support apparatus. There is a single reduced chloroplast in each spermatozoid and numerous (50–100) minute spherical mitochondria, only 0.3 μm diam. These move vigorously in the living cell and when viewed with the light microscope they bear a striking resemblance to bacteria. Rather unexpectedly, no contractile vacuoles could be detected, even though the gametes are naked freshwater cells. Daring spermatogenesis the nucleoli of the vegetative cells disperse and are replaced by a large dense body presumably formed from either nucleolar material or condensed chromatin. The flagellar apparatus includes a cruciate flagellar root system, a feature now known to be characteristic of most green algae, exceptions being those putative ancestors of the higher plants and bryophytes. Discharge of spermatozoids from the antheridia is extremely rapid and the whole process may be finished in 30 sec. The antheridium lacks a pore apparatus, but at maturity bursts open explosively at the apex. Phyletic affinities are discussed and it is concluded that the ultrastructure of the motile cells does not, at this time, support the separation of the siphonous green algae from other green algae into a separate class.     

WILD GAMETOPHYTES OF PHANEROSORUS MAJOR (MATONIACEAE)

The gametophytes of Phanerosorus major collected from wild populations in Seram Island are described. Young gametophytes are slender, ribbon-like and uniformly one cell thick. They develop to old gametophytes with a broad thick cushion and coarsely ruffled wings. The gametophytes are monoecious and protandrous, although archegonia-bearing thalli occasionally become antheridia-bearing. Massive antheridia form on the ventral surface of young and old gametophytes while archegonia are borne on the cushion of old ones. Both young and old gametophytes reproduce vegetatively. The gametophytic characters are compared with those of Matonia. The life cycle of P. major is discussed with reference to its ecology.     

ESTIMATES OF INTRAGAMETOPHYTIC SELFING AND INTERPOPULATIONAL GENE FLOW IN HOMOSPOROUS FERNS

Relatively little information is available on mating systems and interpopulational gene flow in species of homosporous pteridophytes. Because of the proximity of antheridia and archegonia on the same thallus, it has long been maintained that intragametophytic selling is the predominant mode of reproduction in natural populations of homosporous ferns and other homosporous plants. Furthermore, quantitative estimates of interpopulational gene flow via spore dispersal are lacking. In this paper, we examine five species of homosporous ferns (Botrychium virginianum, Polystichum munitum, P. imbricans, Blechnum spicant, and Dryopteris expansa) and present estimates of 1) rates of intragametophytic selling, 2) levels of interpopulational gene flow, and 3) interpopulational genetic differentiation (F_ST). Our data demonstrate that mating systems vary among species of ferns, just as they do among species of seed plants. The data also suggest that levels of interpopulational gene flow are generally high. The F_ST values indicate little genetic divergence among populations for all species except Dryopteris expansa, which exhibits significant levels of interpopulational genetic differentiation. Patterns of genetic diversity in the five species examined are related to the mating system and rate of interpopulational gene flow in each species. The F_ST values for all species except Botrychium virginianum are in close agreement with those predicted for an island model of population structure.     

IDENTITY OF THE ENDOSYMBIONT OF PERIDINIUM FOLIACEUM (PYRROPHYTA): ANALYSIS OF THE rbcLS OPERON1

Extant chromophytic algae have been suggested to have originated via the engulfment of a photo synthetic alga by a colorless protist. The dinoflagellate Peridinium foliaceum (Stein) Biecheler contains a reduced chlorophyll c–containing endosymbiont and, thus, represents an evolutionary intermediate stage in the establishment of chloroplasts. Although the exact phylogenetic relationship of the symbiont to extant algal species is unknown, it had been suggested that the P. foliaceum symbiont was either a diatom or a chrysophyte. Identification of the closest living relative of the P. foliaceum symbiont would provide a free-living model system with which the photosynthetic symbiont could be compared. Nucleotide sequence analysis of rbcL and rbcS (encoding the large and small subunits ofribulose-1,5-bisphosphate carboxylase/oxygenase) by the P. foliaceum symbiont was performed to provide insights into its identity. Cloned restriction fragments from a chloroplast DNA library were screened, and clones encoding the rbcLS operon were sequenced. Parsimony phylogenetic analysis was performed for each gene. Our data strongly suggest that the symbiont originated from a photosynthetic diatom.     

A POPULATION STUDY OF CHARA ZEYLANICA IN TEXAS,OKLAHOMA, AND NEW MEXICO

Examination of 140 collections of Chara zeylanica from 3 southwestern states shows that a strong dichotomy exists in the collections. Some produce 4-plated antheridia while others produce 8-plated antheridia. Absolute separation of the study material is possible on the basis of plate number. In addition, 3 other characters (length/width ratio of oospores; fertility of first branchlet node; and number of distal ecorticate branchlet internodes) show strong correlation with the antheridial type. Preliminary chromosomal work indicates that a segregation at this level may also be possible. In 4-plated collections examined, n = 28; 8-plated collections are usually n = 56; however, a few 8-plated collections are n = 42. No conclusion has been reached regarding the status of the latter collections.     

Characterization of sexual reproductive processes in Chara braunii (Charales,Charophyceae)

Chara braunii is distributed worldwide and is the most common charalean species in Japan. This species is monoecious and produces numerous sets of sex organs, each of which consists of one antheridium and one oogonium, under laboratory culture conditions. In this study, we report that light intensity strongly affected the vegetative phase and sexual reproductive phase of this species. Under high‐light conditions (70.0 μmol photons m^?2 s^?1), thalli grew but did not form reproductive organs. Under a low‐light intensity (10.0 μmol photons m^?2 s^?1), algal bodies formed many reproductive organs. In addition, antheridia without the corresponding oogonia (lone antheridia) were observed under low‐light conditions. The absence of oogonium primordia adjacent to the lone antheridium was confirmed by several microscopic approaches. The addition of liquid fertilizer increased the total number of sex organs and growth; however, the number of lone antheridia decreased with increasing fertilizer concentrations. Exogenously applied gibberellin did not affect the number of lone antheridia. These results suggest that regulatory mechanisms for the appropriate allocation of resources exist in this alga, similar to those reported in some land plants.     

The occurrence of axillary antheridia in dioecious mosses

Abstract

Antheridia that are undoubtedly axillary occur in species of Bryum, Mnium and Aulacomnium. It is suggested that this is a primitive feature and that the typical moss antheridial head, with all the antheridia apparently terminal, has been derived from species with axillary antheridia, either by restriction of the antheridia to the axils of the uppermost bracts, as in the liverwort Haplomitrium blumei, or by the suppression of the upper bracts.     

AN EXPERIMENTAL APPROACH TO THE SYSTEMATICS OF THE MONOECIOUS-CONJOINED MEMBERS OF THE GENUS CHARA,SERIES GYMNOBASALIA

Most monoecious-conjoined members of the series Gymnobasalia, genus Chora, bear either tetrascutate or octoscutate antheridia. A determination of the extent to which various populations of these two morphologically distinct entities are reproductively isolated was the primary objective of the present study. Experimental crosses were attempted between emasculated sprigs and nonemasculated plants serving as sperm sources. All evidence suggests that tetra- and octoscutate populations are reproductively isolated throughout their respective ranges even to the extent of producing black oospores. Crosses were also attempted between geographically isolated tetrascutate, and again octoscutate, populations. All were uniformly successful to the extent that black oospores resulted; but when such oospores were germinated many of the resulting progeny were found to be either nonviable or dwarfed, and frequently self-sterile as well. This was particularly true where parental clones differed with respect to geographical origin, chromosome number, or external morphological features.     

ROLE OF ASYMMETRIC CELL DIVISION IN PTERIDOPHYTE DIFFERENTIATION. II. EFFECT OF CA2+ ON ASYMMETRIC CELL DIVISION,RHIZOID ELONGATION,AND ANTHERIDIUM DIFFERENTIATION IN VITTARIA GEMMAE

Gametophytes of Vittaria graminifolia reproduce vegetatively by means of gemmae. Each gemma consists of a linear array of six cells: four body cells and a knob-shaped terminal cell at each end. When gemmae are shed from the gametophyte onto Knop's mineral medium, the two terminal cells do not divide, but elongate to form primary rhizoids. The body cells undergo asymmetric cell division, and the smaller daughter cells differentiate into either secondary rhizoids or prothalli. When gibberellic acid is included in the medium, antheridia are formed as a result of asymmetric cell division instead of vegetative structures. We studied the effect of Ca²⁺ on asymmetric cell division, rhizoid elongation, and antheridium formation in gemmae cultured on Knop's mineral medium and variations of Knop's medium. Ca²⁺ inhibited the onset of cell division and rhizoid elongation, but was required for differentiation of antheridia. Treatments which lowered the Ca²⁺ content of gemmae (EGTA and dilute HCl extraction, culture on verapamil-containing and Ca²⁺-deficient medium) caused an early onset of cell division and rhizoid elongation. The stimulation of growth was most pronounced when gemmae were deprived of Ca²⁺ during the first 24 hr of culture. The proportion of cell divisions which differentiated into antheridia in response to GA was greatly reduced when the Ca²⁺ status of gemmae was lowered with verapamil and Ca²⁺-EGTA buffers.     

水玉霉(Pilobolus)属的种的重新划分

我们在过去的工作中承认水玉霉(Pilobolus)属的9个种(郑、胡,见戴,1979)。近年来我们重新分离得到了这些分类群并对它们进行了再研究。研究结果表明,尽管它们是彼此可以互相区分的分类群,但是,包括我们过去的概念在内,目前被普遍接受的用于这个属的分类的种概念太小.为了与整个毛霉目的其它属的分类系统相一致,我们把这9个分类群重新划分为由9个变种组成的5个种:晶澈水玉霉原变种[Pilobolus crystallinu (Wigg.) Tode var. crystallinus],晶澈水玉霉透孢变种新组合[P. crystallinus var.hyalosporus (Boedijn) Hu &Zheng, comb. nov.],晶澈水玉霉克莱因变种新组合[P. crystallinus var.kleinii (van Tieghem) Zheng &G.-q. Chen, comb. nov.],豆状水玉霉原变种(P. lentiger Corda var. lentiger),豆状水玉霉小型变种新组合[P. lentiger var. minutus (Speg.) Zheng &G.-q. Chen, comb. nov.],长型水玉霉(P. longipes van Tieghem),厚壁水玉霉(P. Oedipus Mont.),露水玉霉原变种[P. roridus (Bolt.) Pers. var. roridus],露水玉霉突囊变种新组合[P. roridus var. umbonatus (Butler) Hu &Zheng, comb. nov.]。水玉霉属先后报道过的种或种下分类群名称共计50个左右,其中一些异名往往被不同的作者归到不同的正名下面。为了解决它们的正确归属问题,我们对全部原始描述作了细致的文献考证然后决定其位置。对那些找不到原始描述或从原始描述中得不出结论的则作为可疑名称处理。可疑名称共计12个:Mucor obliquus Scop., M. urceolatus Dicks.;Pilobolus urceolatus Purt., P. pestis-bovinae Hallier(=P. hallierii Rivolta), P. nanus van Tieghem, P. intermedius, (Coem.) P. A. Karsten(=P. Oedipus Mont. var,intermedius Coem.), P. pullus Massee, P.proliferens McVickar, P. ramosus McVickar, P. simplex McVickar, P. lentiger forma leinii Reyn. &Laysa, P. lentiger forma minutus Reyn. &Laysa.     

Do motile spermatozoids limit the effectiveness of sexual reproduction in bryophytes? Not in the liverwort Marchantia polymorpha

To test the premise that fertilization distances in bryophytes are limited by spermatozoid motility, we measured the distances between over 80 000 male and female thalli of Marchantia polymorpha on heathland over 2 successive years after a major fire and recorded the incidence of sporophytes. The first comparative data on spermatozoid numbers per antheridium across bryophytes and pteridophytes were calculated from antheridial sizes and spermatid diameters and cross‐checked with the likely numbers produced by successive antheridial mitoses. Individual antheridia of Marchantia produce over 200 000 spermatozoids. Extrapolating from individual antheridia to the numbers of mature antheridia per antheridiophore and then to individual male plants, we calculated that a single flooding event on a male thallus with 10–12 antheridiophores will result in the release of over 50 million spermatozoids. Assuming radial dispersal in surface water films by lipids released from the dehiscing antheridia, spermatozoids can reach distances exceeding 20 m from the parent plants, in line with our finding of 100% fertilization in female plants of Marchantia up to 19 m from the nearest males, far beyond published fertilization distances in dioicous bryophytes. We attribute this to (i) much greater spermatozoid production and numbers in Marchantia than in other bryophytes and (ii) highly effective sperm transport both within the antheridiophores and archegoniophores via their overlapping scales and grooves in the stalks and between male and female thalli via surface water films. These features, coupled with the massive production of small spores, explain the success of Marchantia as the primary colonist of open habitats.