The annual meeting was held on the weekend of 20-21 September in the Plant Science Laboratories at the University of Reading by kind permission of Professor V. H. Heywood. About forty-five members and guests attended on the Saturday when the President introduced six speakers, summaries of whose papers are given here.
Dr. E. V. Watson (Department of Botany, University of Reading):’Changing views on the evolution of the Bryophyta.’
This paper was concerned with ‘macro-evolution’, or the general questions of the origin of the Division Bryophyta and the inter-relationships between major orders of both liverworts and mosses. Attention was drawn to the contrast between the relatively conservative statements which continued to appear in many modern textbooks and the highly iconoclastic views put forward in some contemporary papers. A good example of the latter was ‘A new look at Evolution and Phylogeny in Bryophytes’ by W. C. Steere. The co-existence of so manifestly contradictory statements could only lead to confusion in the minds of students. Examples were given of such contradictions, both as regards putative origins of the group and in connection with evidence for inter-relationships. By contrast, the position some sixty to seventy years ago was seen to have been a much more stable one. Older authors such as Cavers, Campbell and Bower were cited. Whilst adhering to a particular body of morphological evidence in reaching their conclusions, some of these authors (e.g. Cavers) were more cautious in making their pronouncements than they had sometimes been given credit for. The modern tendency was to undervalue morphological evidence and, in extreme cases, to attempt to undermine the basic tenets of morphology. Some reasons for this were sought.
Mr. M. O. Hill (Institute of Terrestrial Ecology, Bangor): ‘Why is Sphagnum considered to be a difficult genus? ‘.
Various inter-related factors have contributed to make Sphagnum difficult in Britain: unfamiliar morphology, out-of-date floras that either lump too much or split too much, great plasticity, and two pairs of taxa that have not been properly understood even by the experts. Plasticity is undoubtedly the basic problem; several pairs of good species can only be separated by ‘soft’ characters, none of which is individually reliable. British sphagnologists have incorrectly interpreted the distinction between S. rubellum and S. capillaceum – which intergrade completely – and between S. auriculatum and S. subsecundum – which, if properly interpreted, are genuinely distinct with no intermediates.
Dr. R. E. Longton (Department of Botany, University of Manitoba): ‘Reproductive biology and evolutionary potential in the Bryophyta’.
Bryophytes are commonly considered to evolve slowly. This paper assesses three factors which have been suggested as important in limiting their evolutionary flexibility, the first being the dominance of a haploid generation incapable of shielding recessive alleles in a heterozygous condition. This consideration applies only to genes expressed in the gametophyte while cytological data raise the possibility that most modern bryophytes may be gametophytically at least diploid following doubling of ancestral chromosome complements. In connection with the second point, that evolutionary potential may have been reduced by a widespread abandonment of sexuality, data are reviewed that suggest that most moss species and many liverworts produce spores in vast numbers at least in part of their range. There is little direct evidence of spore germination leading to establishment of mature gametophytes in the field, but bryophytes which produce spores freely appear in general to be more succ essful than those which do not, suggesting that sexual reproduction is effective in the former group. Thirdly, it has been suggested that inbreeding may severely reduce genetic flexibility in the ca. 50% of mosses and ca. 20% of hepatics which are monoecious. Little is known about population structure and the incidence of outcrossing in such taxa. However, the occurrence of hybrid sporophytes in several groups of monoecious mosses, and the degree of ecological and morphological variation in certain mosses and liverworts, indicate that inbreeding is by no means obligate throughout the monoecious forms. Further studies are required to clarify the issues discussed. Meanwhile, it is suggested that the patterns and processes of microevolution in bryophytes may prove more similar to those in flowering plants than is sometimes supposed.
Dr. N. W. Ashton and Dr. D. J. Cove (Department of Genetics, University of Cambridge): ‘Auxotrophic and developmental mutants of Physcomitrella patens‘.
Thirty biochemical mutants have been isolated in the haploid monoecious moss Physcomitrella patens: five nicotinic acid auxotrophs (nic¯ mutants), four p-aminobenzoic acid auxotrophs (pab¯ mutants), four adenine auxotrophs (ade¯ mutants), two nutritionally dependent strains which are repaired by proline or argenine (prg¯ mutants), three nitrate non-utilizers (nat¯ mutants) and twelve strains which are resistant to the amino acid analogues, D-serine and p-fluorophenyl alanine.
Eight crosses involving six different auxotroph strains, one of which is also chlorophyll deficient (yellow) have been performed. All of the parental strains are self-sterile but cross-fertile in certain combinations. Progeny from the crosses have been analysed but no linkage has been detected. Self-sterility segregates as a pleiotropic effect of the nic and pab mutations.
Two categories of mutants which are abnormal with respect to gametophore production have been isolated. Mutants of one class produce few or no gametophores (gam¯ mutants); mutants of the other class produce many more gametophores than usual (ove mutants). There are two groups of gam¯ strains. Some can be made to produce gametophores, either by culturing them in the vicinity of an ove strain or by the supply of a cytokinin. The other type is unaffected by either treatment.
One cross involving a gam¯ strain has been made. However, most gametophore developmental mutants are sterile. We are therefore attempting to devise a means of genetic analysis, independent of the sexual cycle, which entails the production of diploid protonemata by the fusion of protoplasts.
Professor G. K. Berrie (Fourah Bay College, Sierra Leone): ‘Spore dispersal and perennation in West African species of Riccia‘.
Professor Berrie’s paper is to be published in full in the Journal of Bryology and will, therefore, not be summarised here.
Dr. A. J. Harrington (Department of Botany, University of Ibadan): ‘Vegetational zonation and the bryophytes of West Africa’.
The major vegetation zones of West Africa are determined primarily by climate, in particular by the mean annual rainfall and its seasonal distribution.
In the dry Sahel and Sudan savanna zones, the few bryophytes recorded occur mainly in riverain habitats or as ephemerals which develop during the wet season, e.g. Riccia spp. A more varied bryophyte flora is found in the Guinea savanna zone and includes such characteristic species as Riccia intermedia E. W. Jones and Erythrodontium barteri (Mitt.) Broth. The absence of bryophytes from large areas of savanna is undoubtedly due to the annual burning in the dry season.
In the forest zone, the majority are epiphytic. They can be divided into two groups; sun or high epiphytes which are usually restricted to the crowns of taller trees (e.g. Diplasiolejeunea spp. , Calymperopsis spp.), and shade or low epiphytes which grow on tree trunks and branches in the shade (e.g. Plagiochila spp., many Lejeuneaceae and mosses such as Neckeropsis spp. and Pilotrichella spp.). Bryophytes also occur on living leaves, decaying wood, disturbed soil and termite mounds, and rock outcrops and boulders.
The richest bryophyte assemblages of West Africa are found in forests at altitudes above 1200 m., e.g. in the Loma Mountains of Sierra Leone.
The Annual General Meeting was held after tea. In the evening members were the guests of Professor Heywood and Dr. E. V. Watson at a conversazione at which the following exhibits were displayed:
|Dr A.J.E. SMITH:||‘A comparison of maps showing distributions based upon vice counties and 10 Km grid squares’.
‘A provisional atlas of bryophytes’.
‘A checklist of British mosses – Sphagnaceae to Entodontaceae’.
‘Illustrations for a new British and Irish Moss Flora’.
|Mr. A. R. PERRY:||‘Bryologists at work – photographs from the B. B. S. album’.|
|Dr. H. L. K. and Mrs. M. P. WHITEHOUSE:||‘Aspects of the ecology and distribution of Tortula (Hyophila) stanfordensis‘.|
|Dr. J. G. DUCKETT:||‘Photographs of British bryophytes’.|
|Mr. M. V. FLETCHER:||‘A collection of living Tortulas‘.|
|Dr. E. W. JONES and Dr. F. ROSE:||‘The mystery of Plagiochila ambagiosa solved’.|
|Dr. M. E. NEWTON:||‘Heterochromatin in Pellia‘|
|Dr. E. W. JONES:||‘Some African bryophytes and their distribution’.|
|Dr. E. V. WATSON:||A few thalloid hepatics from the living collections at Reading’.|
The Society is very grateful to Dr. Watson who acted as local secretary, not only for the organisation of this most successful meeting, but also for making the arrangements for members to stay in Reading University’s Wantage Hall over the weekend. This new innovation was very much appreciated by all who took advantage of it.
G. C. S. Clarke
Three localities were visited on the excursion of 21 September. All were in the area W. S. W. of Reading where Tertiary gravels prevail, limiting the flora to more or less acidophile species. Most habitats were abnormally dry after the exceptional summer. The first locality visited was Silchester Common (v.-c. 12), where the most rewarding ground was in the valley bottom. Here Cryptothallus mirabilis was found under birches, seven species of Sphagnum were noted in the bog, including S. nemoreum and S. fimbriatum; and in the alder carr Radula complanata, Pellia neesiana, Chiloscyphus pallescens c. per. +, Acrocladium cordifolium, Ulota bruchii and U. crispa agg. were seen.
At Tadley Common (also in v.-c. 12) the dried-out ‘damp heath’ bore extensive patches of Gymnocolea inflata c. per., Campylopus brevipilus and, locally, Cephaloziella starkei and C. subdentata. In the low-lying boggy western end of the common Sphagnum spp. were locally much intermixed with the liverworts Mylia anomala, Lepidozia setacea (female plants) and Odontoschisma sphagni. Some healthy tufts of Dicranum spurium occurred.
In Wasing Woods (v.-c. 22) only the southern extremity was effectively explored and the ‘moss layer’ was much dried out. The best finds were Leucobryum juniperoideum, growing with L. glaucum (sometimes mixed in a single cushion), and Dicranum polysetum. Liverworts included Calypogeia fissa, C. muellerana, Riccardia pinguis and Scapania undulata, but nothing of great interest. Vegetation on the adjacent gravel-pit area was too undeveloped as yet.
E. V. Watson