In the attractive setting of the Manor Hall of Residence, about fifty members enjoyed what can be fairly described as a bryological compendium, for the programme encompassed a vast range of current activity in the subject. They heard how some of the most modern and sophisticated of techniques have been brought to bear on the meaning of oblique cross walls in caulonemata and of endophytic fungi in hepatics. They heard, also, a critical and useful assessment of additions to the British flora that have been identified by astute observers. Our fascination with the British flora, however, was ably transferred overseas by one of our honorary members, who described his longstanding and continuing interest in liverworts of Africa, and by another speaker, who introduced us to the bryophytes of the Adirondack Mountains. The audience politely accepted a substitute paper on bryophyte sex-chromosomes, and all of us were enchanted by the joint presentation, by two further speakers, of stereoscopic photographs. Summaries of all these papers follow.
Dr. J. Doonan (John Innes Institute): “The microtubule cytoskeleton of Physcomitrella patens.“
Indirect immunofluorescence can be used to visualize the microtubule cytoskeleton of cells within intact colonies of Physcomitrella patens. Microtubules are proteinaceous fibres which – by providing a cytoplasmic scaffold – play key roles in many morphogenetic processes in all eukaryotes. Studies on microtubules in mosses have concentrated on their role in the control of tip growth of protonemata, and how the re-orientation of cross-walls is related to development.
Protonemata grow solely by tip growth: therefore the mechanism by which tip expansion, as opposed to uniform expansion of the entire cell surface, is of interest in terms of morphogenesis. At the tip, microtubules extend into and completely fill the apical dome where they appear to end as foci. When treated with a carbamate herbicide (CIPC) which supposedly interacts with microtubule- organising centres (MTOCs) the tips become swollen, at the same time as the microtubules display aberrant distributions such as asters and starbursts. Disruption of MTOCs, therefore leads to misshapen tip cells
Caulonemata possess oblique cross-walls whereas chloronemata have transverse cross-walls. The process of cross-wall re-orientation, is foreshadowed at anaphase by a large increase in the numbers of spindle pole to cortex microtubules. These are associated with a tilting of the mitotic spindle and this oblique device is then separated by a correspondingly oblique cross-wall. Treatment with anti-MT drugs prevents their appearance, and also prevents the re-orientation. The orientation of the cross-wall is controlled by the direction of light, such that the leading edge of the oblique cross-wall is closest to the light source. During side branching in sub-apical cells, the nucleus returns to the cross-wall and divides so as to form a side branch on the side wall nearest the leading edge of the cross-wall. The side branch is thus initiated in the direction of the light source present when the mother cell was formed. The microtubular cytoskeleton plays a major role in reorientati on of the cross-wall, migration of nucleus to the site of division as well as in division itself.
The study of the cytoskeleton may lead us to a fuller understanding of now the morphology of plants is controlled at the macro-molecular level.
Mr A. C. Crundwell (Headley Down): “The introduced bryophytes of the British Isles.”
We shall never have a complete knowledge of the bryophyte floras of past ages nor learn exactly how those species that did not survive the Ice Age within the British Isles reached these shores. For practical purposes we may accept as native all species that were here before about 1500 A. D., when traffic with North America and South Africa started to become significant.
The evidence that a particular species is an introduction is never direct, but always circumstantial. This evidence is of six kinds:
- Absence of a subfossil record.
- Evidence of a change in geographical distribution. This may take the form of persistence for a few years in one or two localities, followed by disappearance; or of presence in well searched localities where it was not seen before; or of increase in the number of localities, especially when these radiate from a single point.
- Anomalous geographical distribution, either on a world scale, such as the occurrence in England of a Southern Hemisphere species, or locally, such as the occurrence of a species in only one field when there is no conceivable ecological reason why it should not be in others.
- Association with some means of introduction, such as a botanic garden or a port.
- Less than the normal amount of genetic variation in the British population; sometimes in dioecious species only one sex is present.
- Association with open, disturbed or temporary habitats.
Of course none of these criteria is absolute, and there is plenty of room for dispute about the status of individual species.
Thirteen species may be definitely accepted as introductions, or at least as recent immigrants: Riccia crystallina, R. rhenana, Telaranea murphyae, Lophocolea bispinosa, L. semiteres, Atrichum crispum, Campylopus introflexus, Tortula amplexa, T. rhizophylla, Grimmia crinita, Orthodontium lineare, Bryum apiculatum agg. (found on St Mary’s, Scilly, in 1977) and Eriopus apiculatus. There are four more that may well be introductions, but less certainly: Tortula freibergii, Hyophila stanfordensis, Trichostomopsis umbrosa and Gyroweisia reflexa. The four following have been suggested as introductions but are more probably native: Fossombronia incurva, Telaranea nematodes, Campylopus pyriformis and Tortella inflexa. Fissidens lindigii (Hampe) Jaeg. (F. orrii (Lindb.) Braithw.) probably never grew out-of-doors in the British Isles.
A total of seventeen certain or possible introductions is very small in comparison with the large number of introduced angiosperms. This is no doubt mainly because very few foreign bryophytes are deliberately cultivated. Also relevant are the much wider geographical distribution of most bryophyte species, so that incoming propagules must often be those of native British species, and the fact that ports and docks, such a prolific source of alien angiosperms, are relatively inhospitable places for bryophytes and are rarely visited by bryologists.
At least seven of these seventeen species seem to have been introduced independently more than once – perhaps they are associated in their native haunts with favourite horticultural or other imports. Thirteen of them are dioecious and in no less than seven both male and female plants have been introduced; and these grow together except in Telaranea murphyae. Introduction is evidently not always by the single propagule. It is remarkable that seven of these species are found on the Isles of Scilly, five of them being present on the island of Tresco. Planting shelter-belts and making fields and gardens on a barren island creates new ecological niches with no native plants to occupy them but available for colonisation by any bryophytes accidentally brought in when foreign vascular plants are imported.
Dr M. E. Newton (University of Manchester): “Sex chromosome evolution in bryophytes. “
Sex chromosomes in bryophytes are of two types; (1) morphological, of which the X is larger than the Y and also possesses more heterochromatin, and (2) structural, which are seen to differ only in that the Y includes more heterochromatin that the X. In diploid dioecy, where a larger X than Y chromosome occurs, it is usually ascribed to differential erosion of parts of the Y as a result of an increasing genetic load and the absence of crossing-over during meiosis. Difficulties in applying the theory to haploid dioecy have led to the development of several new theories. That of Bull (1978) suggested preferential addition to the X. Like Blute’s (1983) theory, however, it took no account of structural sex chromosomes. Smith’s (1978) theory of Y chromosome deletion, however, while adequate for structural sex chromosomes, did not address the problem of morphological X chromosomes having more heterochromatin than the Y.
A theory to accommodate all known facts relating to bryophyte sex chromosomes (Newton, in press) was therefore put forward. It recognizes the possibility that dioecism may have arisen more than once, essential steps in the argument being that (1) a monoecious gametophyte must have the potential to initiate and develop male and female sex organs, (2) once dioecism arose, the developmental potential of the opposite sex could be seen as redundant and might be suppressed in the form of facultative heterochromatin, (3) there may be more secondary sexual characters associated with femaleness; more heterochromatin could therefore be expected to occur in the male-borne Y- chromosome than in the X, (4) these structural sex chromosomes would be expected to include equal amounts of achiasmate heterochromatin in the sporophyte generation, (5) accumulation of blocks of constitutive heterochromatin could be expected to protect sex-specific genetic information, of which there may be more i n females than in males, (6) erosion of redundant facultative heterochromatin could be expected, there being more in males than in females, (7) the result would be morphological sex chromosomes.
Blute, M. (1983). “Selfish” DNA and differential parental investment: some implications for sex chromosomes. J. theor. Biol. 102, 603-10.
Bull, J. J. (1978). Sex chromosomes in haploid dioecy: a unique contrast to Muller’s theory for diploid dioecy. Am. Nat. 112, 245-50.
Newton, M. E. (in press). The cytogenetics of bryophytes. In The Experimental Biology of Bryophytes (ed. J. G. Duckett and A. F. Dyer). Academic Press, London.
Smith, A. J. E. (1978). Cytogenetics, biosystematics and evolution in the Bryophyta. Adv. Bot. Res. 6, 195-276.
Dr E. W. Jones (Oxford) and Dr A. J. Harrington (British Museum, Nat. Hist.): “African hepatics.”
The coastal regions of West Africa from the Congo to Gambia are in the zone of high rainfall forest: mountains are few. In the forest hepatics are practically confined to tree boles, branches in the canopy, rotting wood, and the leaves of phanerogams and pteridophytes. Some of the species (e.g. Lophocolea spp., Riccardia spp., Aneura, Cephalozia spp.) will be readily recognised by a temperate bryologist as belonging to familiar genera, but the dominant forms belong to genera which will be unfamiliar, with a great preponderance of Lejeuneaceae; out of 67 species collected in the Benin forests in 1947-8 47 were Lejeuneaceae. Species of Plagiochila belonging to sections of the genus characterised by terminal branching (absent from cool temperate climates) are also conspicuous. Further north and south in climates with a strong dry season is savanna, which has been unduly neglected by bryologists. Here the hepatic flora is indeed poorer than that of t he forest zone, but the species are different; they include ephemerals of genera such as Riccia and Fossombronia which grow on the ground during the rainy season.
By contrast the East African lowlands are dry even on the coast, but there are numerous groups of often spectacular mountains arising abruptly out of the arid plains to misty heights where the boughs of forest trees are thickly clothed in Herberta spp., Plagiochila spp., Bazzania spp., and many Lejeuneaceae. Thus the East African hepatic flora is predominantly that of wet mountains whereas that of West Africa is predominantly a flora of wet lowlands; this latter element is almost absent from East Africa.
Some readily recognised and characteristic species of these various floras were illustrated by slides (many of them provided by the British Museum) and also, in an exhibit, by specimens. The exhibit also showed some historic specimens from the British Museum, including those collected by Palisot de Beauvois in Nigeria in 1787-8, the first hepatics ever to be brought back from Africa.
Dr and Mrs H. L. K. Whitehouse (University of Cambridge): “Stereoscopic photography of bryophytes. “
Stereo-photography involves taking two photographs of the subject from slightly different viewpoints. This can be achieved either by using a two-lens camera, or by taking two photographs in succession with an ordinary single-lens camera and displacing the camera between the exposures. Photographs taken by both methods were shown. The displacement method has the disadvantage that any movement of the subject in the interval between making the two exposures becomes evident. On the other hand, standard stereo cameras available on the market have the lenses set at the average human eye separation, which results in distortion if the subject is closer than 2 m. Yet it is close-up stereo photography that is so rewarding and which is needed in any case for small objects such as bryophytes. The lens separation then needs to be one thirtieth of the distance of the subject. Thus, with a moss 15 cm from the lens, the camera needs to be moved laterally 5 mm before taking the second photo graph. Many of the close-up photographs shown were taken with a home-made stereo camera with adjustable lens separation.
For showing stereo-photographs a twin-lens projector was used containing polarized filters and the audience wore spectacles with complementary filters. A metallic screen is necessary. A diverse range of bryophytes was shown, including views of the habitat of some species. Stereo-photography is valuable in enabling one to become familiar with the field appearance of the plants, both when wet and when dry. It also allows one to visualize how species compete: for example, Eurhynchium striatum, Brachythecium rutabulum and E. praelongum were seen in one photograph interwoven in a complex way on a woodland floor. In conclusion, a few stereo-photographs of bryologists were shown.
Dr K. Pocock and Prof. J. G. Duckett (Queen Mary College, London) “The alternative mycorrhizas: fungi and hepatics.”
By contrast to the lack of intimate relationships between mosses and microorganisms, endophytic fungi are widespread in hepatics. Light and electron microscope studies have revealed these associations to be of three main types which almost certainly evolved independently in different groups of liverworts.
Basidiomycetous mycelia are invariably present in the stems and rhizoids in the majority of British members of the Jungermanniaceae and in other genera scattered through other families in the Jungermanniales (Marsupella, Saccogyna, Harpanthus, Southbya, Ptilidium). Amongst thalloid taxa this type of association is limited to the Aneuraceae and is highly developed only in Cryptothallus. The hyphae, with dolipore septa, but lacking clamp connections, form intracellular coils or pelotons within liverwort cells. Unlike the mycorrhizas of higher plants the fungus does not spread between the host cells (most likely a reflection of the absence of intercellular spaces in hepatics) but penetrates directly through the cell walls in the stems and extends into the substratum only via the rhizoids. Meristematic tissues, gametangia and sporophytes remain free from fungus. The distribution of the fungus is characteristic of each species. In Southbya it is restricted to a strand of cells running down the centre of the stems but in Tritomaria and Lophozia the ventral side of the stems contain a mosaic of infected and uninfected cells. A notable feature of the last two genera is the production of papillae projecting into uninfected cells from the walls contiguous with those containing the fungus. These wall ingrowths consist of fungal hyphae surrounded by liverwort wall material. The hepatic-fungus interface is highly reminiscent of that in vascular plant mycorrhizas with both partners possessing a normal complement of organelles.
The fungi found in British Marchantiales (except Ricciaceae where they are absent), and in Fossombronia, Petalophyllum and Pellia (Metzgeriales) are closely similar to those forming vesicular arbuscular mycorrhizas in vascular plants. An intramatrical mycelium comprises large trunk hyphae which give off profusely branched arbuscules. The fungi possess the distinctive reticulate vacuolation found in Zygomycetes and many vacuoles containing polyphosphate granules.
In the third kind of association, found in the Lepidoziaceae, Calypogeiaceae, Cephaloziaceae and Mylia anomala, the fungus is largely restricted to the rhizoids. The hyphae in Calypogeia proliferate in the basal parts of the rhizoids whose adjacent stem cells possess numerous wall ingrowths each comprising a hypha overgrown by hepatic wall materials. In other genera the fungi form dense coils within swollen rhizoid apices. These are especially numerous on underground axes which extend to depths of up to 20 cm in peaty substrata.
Mr A. R. Perry (National Museum of Wales): “Incursions into the North American bryoflora.”
Remarks were mostly confined to a comparison of the mosses of the British Isles with those of New York State, more specifically the Adirondack Mountains. The history of bryophyte study and collection in the State goes back to about 1830, but the first published work did not appear until 1866 when C. H. Peck listed 274 mosses and 66 liverworts. Over one hundred years later, in 1980, E. H. Ketchledge published his Revised Checklist of the Mosses of New York State which includes about 500 taxa. No similar published checklist of hepatics of New York is known to exist though Schuster’s The Hepaticae and Anthocerotae of North America, when completed, should provide one. A quick count in Ketchledge’s List reveals about 180 species not recorded in the British Isles. Taking the moss flora of the British Isles as about 700 taxa these figures indicate that there are about 380 taxa in the British Isles not recorded in New York State.
There is, though, a considerable common element in their moss floras and a British bryologist visiting New York State for the first time will experience a certain amount of familiarity with its bryoflora. There are, however, some pitfalls for the incautious. For example the common Hypnum is not H. cupressiforme nor H. mammillatum butH. pallescens (Hedw.) P. Beauv., though the differences may be subtle; the common woodland Thuidium is not T. tamariscinum (which is not recorded) but T. delicatulum; Mnium hornum is present, but is essentially montane; there are two species of Climacium, C. dendroides and C. americanum Brid., the latter rather commoner; Paraleucobryum longifolium, seen recently in the British Isles only on Cairngorm, is common on acid rocks in lowland forest; Thamnobryum alopecurum is absent, being “replaced” by T. alleghaniense (C. M.) Nieuwl.; Pseudolesk eella nervosa, a very rare montane saxicole in Britain is frequent on tree bases and logs in lowland forest in New York State.
Several genera absent from the British Isles are represented. For example, Thelia, placed by Crum & Anderson in their magnificent Mosses of Eastern North America (Columbia University Press, 1981), in the Leskeaceae with, i.a., Anomodon and Pterigynandrum, is characterized by laminal cells with very long and often branched papillae and usually spinose to ciliate leaf margins. Its three species grow usually on tree bark where they form light- to glaucous-green creeping mats. Forsstroemia, represented in the area by F. trichomitria (Hedw.) Lindb., is probably related to Cryphaea and like it usually grows on tree bark, but it superficially resembles a Leucodon. Drummondia, named after the Scottish botanist Thomas Drummond, is represented by D. prorepens (Hedw.) E. G. Britt. It is a member of the Orthotrichaceae but has long creeping stems with ascending branches. A species that may occur in the British Isles is Anacamptodon splachnoides (Froel. ex Brid.) Brid., commonly called the “knothole moss” from its propensity for growing in often wet or water-filled knotholes on tree trunks, often on Fagus spp. Its gametophyte is nondescript and therefore easily overlooked, resembling a rather scruffy Amblystegium; but it is frequently fertile when its capsule offers distinct features for recognition. Another possible British species is Sphagnum pylaesii which in the northern part of its range is often submerged in shallow pools near sea-level, but farther south, as in the Adirondacks, is often in montane habitats on granite rocks wet by seepage but not submerged.
The Annual General Meeting was held afterwards (Minutes in Bulletin 46) and was succeeded in the evening by a conversazione, during which the demonstrations listed below were displayed. Throughout the whole of the meeting, Dr D. C. Lindsay rendered invaluable service as local secretary. That he did so with unfailing good humour is a matter for admiration, and the Society is greatly indebted to him.
|Dr R. Alexander:||Some bryophyte microhabitats in the Burren.|
|Mrs J. Appleyard, Dr M. O. Hill and Dr H. L. K. Whitehouse:||Leptobarbula berica (De Not.) Schimp. in England.|
|Prof. E. G. Cutter:||Scanning electron microscopy of bryophytes.|
|Mr R. J. Fisk:||Reading Circle.|
|Dr S. W. Greene and Mr L. T. Ellis:||B. B. S. bryohistorical project.|
|Miss J. Ide:||Mosses with 8-year olds.|
|Dr E. W. Jones:||African hepatics.|
|Dr M. E. Newton:||Liverwort chromosome banding.|
|Dr M. C. F. Proctor:||Scanning electron micrographs of peristomes.
Waxy cuticles on leaves of Polytrichaceae.
|Mrs P. M. Whitehouse and Dr H. L. K. Whitehouse:||Stereoscopic photographs of bryophytes.|
Field meeting – Wyre Forest
After torrential rain on the day of the Paper-reading meeting, participants in the field excursion on Sunday were able to enjoy a day of fine weather. About 25 members gathered, and were guided by Mr Peter Thomson to sites in the Wyre Forest, an area which has been fairly thoroughly investigated for bryophytes. Most people spent the morning searching along the banks of the stream in Park Brook valley and saw: Frullania tamarisci, F. dilatata, Trichocolea tomentella, Pellia endiviifolia, Hypnum lindbergii, Ulota crispa, Amblystegium tenax and a patch of Ctenidium molluscum assigned to the “woodland taxon”.
Members gradually emerged from the stream valley to have lunch beside the path of the old railway line, before a somewhat depleted party set off at a more rapid pace towards Dowles Brook and Lords Wood valleys. The excursion provided several members with an opportunity to return to old haunts: Drs Longton and Greene visited a site where 15 years before, sporophytes were produced by Pleurozium schreberi following the transplantation of male plants, finding no trace of either sporophytes or male plants, but Martha Newton was able to locate a fine colony of Bazzania trilobata on a well-remembered boulder beside the path to Dowles Brook. Additional species recorded in the afternoon included Cephaloziella divaricata, Saccogyna viticulosa and Plagiothecium undulatum, and the list was enhanced by a new Vice-county Record provided by Jean Paton who discovered Jamesoniella autumnalis on a Sorbus torminalis trunk in the valley below Lords Wood.