The paper-reading meeting on the weekend of Sept 25-26 in Ancaster Hall, University of Nottingham, attracted an attendance of nearly fifty members and friends, including two from overseas. They heard a series of well-presented papers covering a particularly wide range of bryological topics. Thus, the proceedings opened with a more detailed account of the chromosomes of certain members of the Brachytheciaceae than any so far available. Another paper, drawing Phylogenetic conclusions from biochemical data, was presented in such a way that even those of us who may be bewildered by chemical formulae were able to appreciate the fine points of the persuasive new arguments put forward. Yet another engrossing talk took the form of a guide to classical bryological literature and stimulated an awareness of the development of the art of illustration. It was a theme related to that of another speaker who involved his audience in an interesting exercise designed to estimate the ext ent to which photography can substitute for bryophyte collecting. The remaining papers, however, were all concerned with various aspects of reproduction and development. One concentrated attention on problems of reproductive behaviour in mosses, while another probed the influence of light on the development of liverwort setae and archegoniophores and the third, using electron microscope techniques, investigated the role of microtubules in bryophyte spermatogenesis. Summaries of these papers are given below.
Dr. S. V. McAdam (Aberdeen) “Karyotype variation in the Brachytheciaceae: a pattern of relationships.”
The work embodied in this paper is to be published in the Journal of Bryology.
Mr. C.C.J. Miller, Prof. J.G. Duckett (Queen Mary College, London) and Z. B. Carothers (Illinois): “Experimental studies of spermatogenesis in bryophytes.”
The highly differentiated spermatozoids of bryophytes are excellent vehicles for investigating many fundamental problems of cell biology including the manner of growth of microtubules and their precise role in subcellular shaping processes. Using antitubulin raised against porcine brain tubulin immuno-cytochemical tests on Sphagnum and Polytrichum provide the first direct evidence that the cytoskeletal band of microtubules, or spline is composed of tubulin. Intense fluorescence from the lamellar strata of the multilayered structure (MLS) strengthens the notion that these are a highly structured microtubule organising centre (MTOC) as does the substructural modification of the lamellae by griseofulvin, an inhibitor considered by some to affect MTOCs.
Having thus established the basic chemistry of the spline the microtubule inhibitor colchicine was used to determine the direction of assembly of the tubules. The occurrence of late spermatids of Pellia with a normal MLS and flagellar bases at the anterior end but grossly distorted nuclei lacking a spline indicate that the microtubules assemble at their posterior ends. Since the elongation of the spline precedes that of the nucleus, growth of its microtubules cannot be the force generating system responsible for shaping the gametes. More likely the spline acts as a cytoskeletal alignment system. Bundles of microfilaments adjacent to the spline (revealed for the first time in plant spermatids (Petalophyllum) by new fixation procedures) are by far the most likely candidate for the force-generating elements.
Spermatozoids of Marsupella and Sphagnum have been fractionated by treatment with non- ionic detergent and sonication. The nucleus is readily separable from the spline in Marsupella but remains attached much more firmly in Sphagnum. High resolution electron microscopy of negatively stained preparations reveals that the firmer adherence in Sphagnum is associated with more highly decorated tubules than those of the spline in Marsupella. A sheath of 30nm filaments is unique to the spermatozoids of Sphagnum and underlines the separation of the genus from all other groups of bryophytes.
Dr. D. H. Lewis and Dr. A. Christie (Sheffield): “The phylogeny of leafy liverworts in relation to their success as land plants.”
Compared with the check list of Jones (1956), the new census catalogue of British hepatics (Corley & Hill, 1981), based on the classification of Grolle (1976), arranges British leafy liverworts into substantially more families and into a different sequence. With regard to British families, the scheme of Schuster (1979) has approximately the same number as that of Grolle but the order in which families are listed is essentially its reverse. Owing to the inherent problems of inferring phylogenetic relationships from linear lists, a representation for leafy liverworts similar in style to that of Dahlgren (1977) for angiosperms was constructed based on the distribution of 4 kinds of soluble carbohydrate – sucrose, sedoheptulose, and six- and seven- carbon sugar alcohols. The scheme supported the phylogenetic arrangement of Schuster (1966 and 1972) and implies a progressive evolutionary loss of the capacity to accumulate free sedoheptulose, heptitols and hexitols. These are abu ndant in genera, such as Herberta and Bazzania, considered by him to be primitive and absent in genera such as Porella considered by him to be advanced.
These conclusions were examined in relation to the hypothesis that the essential role of boron in plants concerns synthesis of lignin and that possession of sugar alcohols, which complex borate, precludes the development of this capacity (Lewis, 1980). It was argued that development of a lignified vascular tissue as an adaptation to life on land could therefore not have occurred in primitive leafy liverworts but that, in more advanced groups which lack sugar alcohols, this may now be possible. The presence of brittonins, methoxylated aromatic compounds, in Frullania (Asakawa, Tanikawa & Aratani, 1976), a genus in which hexitols are absent or in low concentrations, could support this hypothesis if their biosynthesis involves a boron-dependent metabolism related to that proposed for precursors of lignin. These speculations highlight the necessity to study the boron-requirement of bryophytes in general. None appear to have been made.
Asakawa, Y., Tanikawa, K. & Aratani, T. (1976) New substituted bibenzyls of Frullania brittoniae subsp. truncatifolia. Phytochem. , 15, 1057-1059.
Corley, M. F. V. & Hill, M. O. (1981) Distribution of Bryophytes in the British Isles: a census catalogue of their occurrence in vice-counties. B. B. S., Cardiff.
Dahlgren, R. (1977) A commentary on a diagrammatic presentation of the angiosperms in relation to the distribution of character states. Pl. Syst. Evol., Suppl. 1, 253-283.
Grolle, R. (1976) Verzeichnis der Lebermoos Europas und benachbarter Gebiete. Feddes Rep. 87, 171-279.
Jones, E. W. (1958) An annotated list of British hepatics. Trans. Br. bryol. Soc. 3, 353-374.
Lewis, D. H. (1980) Boron, lignification and the origin of vascular plants – a unified hypothesis. New Phytol., 84, 209-229.
Schuster, R. M. (1966) The Hepaticae and Anthocerotae of North America East of the Hundredth Meridian, Volume I, Colombia University Press, New York.
Schuster, R. M. (1972) Phylogenetic and taxonomic studies on Jungermanniidae. J. Hattori bot. Lab. 36, 321-405.
Schuster, R. M. (1979) The phylogeny of the Hepaticae. In: Bryophyte Systematics. (Ed. G. C. S. Clarke and J. G. Duckett). Pp. 41-82. Academic Press, London.
Prof. J. G. Duckett (Queen Mary College, London): “Does photography render the collection of bryophytes unnecessary?”.
Although the most serious threat to the British Bryophyte flora is the rapid loss of natural and semi-natural habitats (H. J. B. Birks, Bull. Br. bryol. Soc. 1982, 39, 17-18) potential dangers from collecting should also be considered. In contrast to the situation with groups of organisms such as birds or vascular plants which may, with practice, be identified in the field, the acquisition of bryological competence depends on regular collecting. The healthy state of the British Bryological Society, and our detailed knowledge of the bryophyte flora, owes much to the tradition of field excursions and collecting. Paradoxically collecting may also serve the interests of conservation. Preservation of mosses and liverworts whose value is cultural, scientific-educational and aesthetic-recreational (Birks, l.c. 1982) rather than of direct economic importance, depends heavily on the efforts and information provided by active bryologists. Any extensive ban on colle cting would be marked by a dangerous decline of interest in bryophytes.
It is axiomatic that beginners must collect virtually everything in order to become familiar with the flora. Ultimately however every experienced bryologist must carefully examine his or her need for collecting, particularly when rare and/or endangered species are involved. The following table is a highly subjective attempt to categorize how I, as a fairly active bryologist with some 20 years experience in the field, identify British bryophytes.
|Identification category||No. of species||%||%|
|Musci (684 spp.)|
|Immediately recognisable to the naked eye|
|Collecting potentially harmful||50||7.3|
|Recognisable using a hand lens|
|Collecting potentially harmful||163||23.8|
|TOTAL recognisable in field||498||72.8|
|Microscopic examination highly desirable or essential|
|Collecting potentially harmful||138||20.2|
|Hepticae and Anthocerotae (234 spp.)|
|Immediately recognisable to the naked eye|
|Collecting potentially harmful||25||8.8|
|Recognisable using a hand lens|
|Collecting potentially harmful||66||23.3|
|TOTAL recognisable in field||213||75.0|
|Microscopic examination highly desirable or essential|
|Collecting potentially harmful||44||15.5|
It is clear from the table that approximately 25% of the flora MUST be collected for identification. This chiefly includes taxa whose recognition depends on characters such as peristome structure, spore morphology or cell sizes. The subdivision of each category into “common” species and those where collecting may be harmful focuses attention on the fact that there are a large number of species where it is difficult to justify repeated gatherings just to fill one’s herbarium. However, multiple packets of some uncommon species can prove extremely valuable providing that the collecting has been done carefully. For example a packet containing plants with a range of morphology, sex organs and sporophytes provides basic information on reproductive biology.
The habits of bryologists in the field may be far more damaging to the flora than the actual removal of material for herbarium specimen. Devastation of Sphagnum lawns in the search for Cryptothallus is a particularly horrendous example. Some plants may be replanted after cursory examination with a hand lens, whilst others are doomed (e.g. Lejeuneaceae closely adhering to rock faces and tufts of saxicolous Grimmiaceae on dry rocks). Whereas there is little or no risk in collecting from arable fields where survival depends on the spore or gemma bank, removal of spring annuals from shallow soils overlying limestone may also destroy a habitat plus the spore reservoir which has taken many many years to form. These examples illustrate why bryologists must always be sensitive to the nature of any habitat they are exploring. On balance the value of collecting bryophytes far outweighs the potential dangers so long as each individual exercises restraint and common sense.
Members were invited to attempt the identification of 30 hepatics and 50 mosses from colour slides. The results, which perhaps provide the most telling answer to the question posed in the title of this paper, are as follows:-
|No. of returns 36|
|Hepatics:||Mean 13 (39%), range 2-28|
|Mosses:||Mean 22 (45%), range 5-42|
Prof. Elizabeth G. Cutter (Manchester): “Growth and response to light of archegoniophores and setae of liverworts.”
The setae of Pellia and other liverworts and the archegoniophore stalks of Conocephalum (and Marchantia) showed a positive response to unilateral light from the blue region of the spectrum. Decapitation did not prevent the response; the regions of perception and response are probably the same. Unilateral light appeared to result in promotion of growth on the darker side, probably with some inhibition on the side towards the light.
Experiments in which the setae were marked with anion exchange resin beads showed that growth was uniform over the entire length, whereas in the archegoniophore stalks much more elongation occurred in the region just below the cap. Elongation involved cell division as well as cell extension, and an intercalary meristem appeared to be present in the upper part of the stalk. Removal of the cap resulted in an 8 to 20-fold decrease in growth in the upper region, suggesting that the cap (possibly the developing embryos) supplies a stimulus to growth of the stalk which bears it.
Mr. C. J. Miles (Reading): “Studies on the reproductive biology of British mosses.”
Most moss species produce sporophytes in at least parts of their ranges. However, little is known of the frequency with which gametophytes become established from spores in the field or of the extent of self-fertilisation in monoecious taxa, both matters of considerable significance in terms of the evolutionary mechanisms open to mosses. This is a preliminary report of an investigation into these aspects of the reproductive biology of five mosses, Atrichum undulatum, Bryum argenteum, Grimmia pulvinata, Polytrichum alpestre and Tortula muralis.
Analysis of regular collections from several British populations of each species has confirmed that fertilisation and spore release show seasonal periodicity. Colony development and longevity is being studied by repeated photography of permanent quadrats, while counts of sporophytes in the quadrats have yielded estimates of annual capsule production per m² moss cover ranging from c. 800 in A. undulatum to c. 88,000 in T. muralis. These data, combined with haemacytometer estimates of spore content in individual capsules, indicate that spore output per m² moss cover may range from 116 x 106 in A. undulatum to 38,325 x 106 in T. muralis. Spores of the five species germinate freely on agar and also on natural substrata under laboratory conditions, giving protonemata and eventually shoots.
Spores were trapped at various distances around an isolated, transplanted colony of A. undulatum throughout the 1982 winter dehiscence period using vaseline coated slides. Of the 18,360 spores trapped (0.04% of the estimated total released), approximately 95% were caught on the ground beside the colony with a few caught up to 150 cm distant. Previous observations had also shown the occurrence of numerous spores in and around A. undulatum colonies after dehiscence.
Examination of young shoots of A. undulatum and other species in the field has demonstrated that many arise by vegetative propagation. No naturally occurring shoots had clearly arisen via protonemata from spores, although the origin of many of those examined was obscure. Occasional spores recovered from soil near colonies of A. undulatum had germinated but no protonemata comprising more than 5 cells were seen. Experiments have been conducted to compare establishment of colonies from spores and by regeneration from portions of gametophyte by planting both at field sites. Methods for planting spores include their application in concentrated aqueous suspension, immersion of undehisced but artificially opened capsules near the soil surface, and planting net bags containing spores and substrate into the field substrate. Regeneration of new shoots from gametophyte fragments occurred readily in A. undulatum and B. argenteum on soil and in P. alpestre on Sphagnum. Gametophyte fragments of G. pulvinata and T. muralis placed or glued onto concrete consistently blew away. Only once however has the occurrence of spore germination been confirmed, when protonemata and shoots developed in net bags containing spores of A. undulatum. Spores of P. alpestre recovered from net bags placed in Sphagnum remained viable but ungerminated for up to one year. An attempt is being made to determine when establishment from spores is blocked, by planting out simultaneously freshly sown spores, germinated spores, protonemata and protonemata with shoots, the older stages having been raised in the laboratory.
A study of sex distribution in A. undulatum and T. muralis has shown that although both are monoecious most shoots develop gametangia of only one sex during one reproductive cycle. Of over 100 young sporophytes of both species examined, 76% in A. undulatum and 96% in T. muralis were on shoots without current cycle antheridia. Thus crossing between shoots within colonies clearly occurs frequently in these species. The extent to which individual colonies comprise several clones, thus permitting genetically effective outcrossing is currently being investigated.
The study species thus produce viable spores in profusion and a prevalence of self-fertilisation in the monoecious species cannot be assumed. The results suggest that asexual reproduction may be more important than reproduction by spores in maintaining populations of the study species. Further work is required to show whether sexual reproduction plays some role in population maintenance, or in establishing colonies in new areas.
Mr. M. Walpole (Loughborough): “A bibliophile’s view of bryological literature.”
A brief review was given of a number of important illustrated works relating to the history of bryology. Particular emphasis was given to the important and finely illustrated works of Hedwig together with examples from the often overlooked English literature of the middle 19th century. The importance of published Exsiccatae was also covered and examples of photographs of early bryologists contained in a copy of Braithwaite’s “Sphagnaceae Britannicae Exsiccatae” were shown.
The Annual General Meeting (Minutes in Bulletin 42) was held afterwards and was followed by a reception given by the University, during which the President thanked Dr. J.O. Rieley for his efforts as local secretary in contributing so much to the success of this meeting. The evening continued with a conversazione and an opportunity to display a large number of exhibits as follows.
|Mr. A.D. Banwell:||Antiquarian bryological literature.|
|Dr. A. Christie and Dr. D.H. Lewis:||Chemotaxonomy and phylogeny of leafy liverworts.|
|Dr. S.W. Greene:||International Association of Bryologists.|
|Mr M.O. Hill:||B.B.S. mapping scheme
Computerized census catalogue.
|Mr. P.J. Lightowlers:||A new section of Tortula?|
|Dr. M.E. Newton:||Meiotic aberration and reproductive performance in the moss Hookeria lucens.|
|Mr. B.J. O ‘Shea:||Microcomputer assistance with a small herbarium – the “Bacchus” system.
B.B.S. reading circle.
|Dr. M.W.S.J. Van Slageren:||A taxonomic monograph of Brachiolejeunea (Hepaticae).|
|Dr. H.L.K. Whitehouse:||Sealed cultures of mosses.|
Field meeting, September 26th, 1982
26th September, 1982. The weather was cool but otherwise fine for our trip. We assembled at Ancaster Hall at 9.30 a.m. on Sunday morning and set off in convoy for Hilton Gravel pits, a Derbyshire Naturalists’ Trust reserve on which almost no previous bryophyte recording had been carried out (i.e. only 9 species). The site provides a contrasting selection of habitats including disturbed ground, grassland, arable land, water, swamp and a small area of very wet fen with incipient Sphagnum bog. We increased the number of species recorded for the site to 52! No surprises were found, but we worked up an appetite for lunch.
In the afternoon we spent two hours wading up to our knees in the very wet peaty surface of Chartley Moss, N.N.R., in Staffordshire. This very interesting basin mire had been visited by the B.B.S. once before in 1973 and the number of species recorded on this visit (19) was disappointingly lower than the previous one (73). We did, however, add one new record, Cladopodiella fluitans, to the list! Most members were more interested in the ecology of the site which has a number of unique features.