A total of 54 members and guests met at Hulme Hall in the University of Manchester for all or part of the autumn paper-reading and annual general meeting, held during the weekend of 22-23 September. We were particularly pleased to welcome a number of new members attending their first meeting of the Society, and to have three overseas visitors. The participation of several members of the Manchester Department of Botany, including three of its professors, was also very welcome.
On the Saturday, the President and Vice-President introduced six speakers whose papers reflected an increasing awareness of the desirability of more experimental work on bryophytes, a trend which was applauded by the Society during its international symposium in Bangor. Thus, we heard accounts of genetical, morpho-genetical, biochemical and ecological experiments which, apart from their intrinsic interest, served to emphasize the morphological implications of physiological and behavioural characters. Summaries of these papers are given below.
Mr. P. M. Hayward and Dr. R. S. Clymo (Department of Botany, Westfield College, London): “The growth of Sphagnum: effects of environment. “
Two aspects of the environment were considered: water and light. An important feature of these is that they affect the growth of different species in different ways. This point was illustrated with some results from a factorial growth experiment which combined the effects of shade and water level on two species: Sphagnum rubellum and S. papillosum. Growth in mass increased with more light for both species but S. papillosum was more tolerant of higher water levels. Conversely, shading caused the plants to grow longer and become etiolated.
Both water and irradiation affect the plants by acting on the apical growing region. Water gets to the apex by capillary action in the small spaces between plants so that an individual will receive less water when growing above the general surface and more water below. The reverse is true of irradiation which will be reduced below the surface due to shading by neighbouring plants. It was demonstrated that this shading effect followed Beer’s Law with absorbance being proportional to depth. In general, S. rubellum attenuated light more strongly than S. papillosum but the exact amount depended on the previous growth history.
A method for measuring profiles of water content in peat was also described. This utilized the attenuating effect of water on gamma radiation. It was demonstrated that the capillary spaces in S. rubellum were smaller than in S. papillosum allowing it to maintain a similar water content in the apex even with lower water-tables. However, the actual moisture profile depended on whether the water-table was raised or lowered to a particular position. This hysteresis effect was often as great as the differences between species.
Finally, a tentative model incorporating these various effects was described.
Miss O. M. Bragg (Department of Biological Sciences, University of Dundee): “The water relations of Sphagnum communities.”
This paper was concerned with the water economy of the surface layers of Dun Moss, a raised bog in the Grampian foothills. The vegetation consisted largely of Sphagnum species, which formed a characteristic mosaic of hummocks and hollows. The seasonal behaviour of the water table in relation to these elements of microrelief was described. It emerged that there were significant differences in the response of the water table to varying meteorological conditions, both between adjacent hummocks and hollows, and between hummocks of S. magellanicum and S. capillifolium. Scanning electron micrographs were presented to illustrate the capacity of individual Sphagnum shoots to retain and conduct water. Microscopic examination of thin sections cut from intact stands of the two species indicated that there were obvious differences in pore structure between associations of their living shoots, but that these differences disappeared within 20 cm of the surface as a result of humification. The spatial variations in structure were reflected by variations in horizontal hydraulic conductivity, whose value at the surface was much greater in S. magellanicum stands, but which decreased exponentially with depth in areas of both species. The greater seasonal variability of water table relief observed in S. capillifolium stands was attributed to the comparatively high resistance to horizontal flow within them. Finally, the possible bearing of pore structure on the rate of vertical water movement, and the effect of the presence of vascular plants, were discussed.
Dr. D. H. brown and Dr. G. W. buck (Department of Botany, University of Bristol): “The cation content of bryophytes.”
Much recent work on the cation content of bryophytes, under natural and polluted conditions, has failed to determine the cellular location of specific elements. Only material within the cell (plasmalemma) can have an immediate effect on metabolism.
A sequential cation elution technique was described, separating four cellular compartments: 1) intercellular soluble, 2) extracellular exchangeable (nickel usually used as the displacing agent) = cell wall, 3) intracellular soluble and 4) residual. Generally, in washed material, potassium and sodium are mainly located in 3 but after sea water treatment non-halophytes show increased sodium in 2 and 3 (potassium in 3 decreases) while halophytes show slight increases in 2. Depending on the species, calcium is present in either 2 and/or 4 and magnesium and zinc show patterns intermediate between calcium and potassium (i.e. in 2, 3, and 4).
Following desiccation stress (storage at 52% and 0% RH) potassium leaks from 3 mainly into 1 while soluble magnesium may be trapped in 2. The degree of potassium loss has been used as a measure of membrane damage and reflected the depth and duration of desiccation, species used, water availability in the habitat and availability of metabolisable reserves to repair membrane damage.
After exclusion of particulate matter material from heavy metal rich sites showed almost identical cellular locations for strontium and calcium (Brachythecium rutabulum), copper mainly (Solenostoma crenulatum) and lead exclusively (Grimmia donniana) in 2.
Dr. C.J. gliddon (School of Plant Biology, University College of North Wales, Bangor): “Studies on the population biology of four species of thallose liverwort.”
Natural populations of four species of thallose liverwort (Pellia epiphylla, Conocephalum conicum, Lunularia cruciata and Marchantia polymorpha) were collected from sites throughout Britain. The populations sampled were all riparian and at least two of the species under study were always present in populations sampled. In this way it was hoped to minimise any differences between species which were a result of differences in their physical environment. Populations of the four species were assayed for protein polymorphism using polyacrylamide gel electrophoresis (PAGE). Eight specific enzyme stains were used, which on subsequent genetic analysis yielded data on between 24 and 61 loci, depending upon the species. Estimates of genetic variability in the four species were made (average number of alleles per locus, and the proportion of loci polymorphic). In addition a theoretical estimate was made of the average amount of heterozygosity (H) on the assumption that the haploid gametophyte mated at random to form a diploid sporophyte. This was to allow a direct comparison with the literature for higher plants and animals. Estimates of genetic distances between populations were also made.
In comparison with higher plants, the thallose liverworts were genetically uniform (H = 0.020 for liverworts, H = 0.108 for 2 species of higher plant). The four liverworts divided into two groups on the basis of variability: P. epiphylla which was genetically uniform (H = 0 ± 0.000) throughout the British Isles; L. cruciata, M. polymorpha and C. conicum which possessed low levels of genetic variation (H = 0.026 ± 0.005). This grouping is in accord with the taxonomic relationships of the four species, P. epiphylla being relatively distantly related to the other three which are all placed in the same super-genus.
The data on genetic distances were only calculated for between-population, within-species comparisons,due to the difficulties with the PAGE-technique of assigning identities to bands which migrate the same distance in different species. Due to their genetic uniformity, P. epiphylla populations of course had a genetic distance of 0 between them. A Canadian population of P. epiphylla was obtained, giving a genetic distance of 0.14 from the U.K. populations. This distance was of the same order as that obtained between populations of the other three species, some populations of which were only separated by about 400 metres. This illustrates the difficulties of utilising genetic distance measures derived from PAGE in taxonomic analysis, as fundamental life-history and genetic parameters may strongly bias the magnitude of such estimates.
Work is in progress to assess the levels of genetic variation in two other species of the genus Pellia (P. endiviifolia and P. neesiana) to see whether the lack of genetic variability in P. epiphylla is a facet of its particular life-history or of the genus as a whole.
Dr. L. P. Nyman and Prof. E. G. Cutter (Department of Botany, University of Manchester): “Control of bud outgrowth in the gametophore of Plagiomnium. “
In growing shoots of P. cuspidatum and P. undulatum an inhibited bud meristem was present on the stem above each leaf axil. Following decapitation, several buds in upper axils grew out; others were activated, but were re-inhibited by growing buds. Applied auxin failed to inhibit buds in decapitated shoots completely, but after treatment with some concentrations they developed as spherical structures devoid of leaf primordia. Cytokinins permitted initial bud development, but completely inhibited later development. Auxin and cytokinin applied in combination yielded buds which morphologically resembled those which had been released and then re-inhibited naturally.
Enzyme histochemistry of released and inhibited buds suggested that oxidation processes may be important in maintaining bud inhibition in intact gametophores. Further investigations of enzyme histochemistry and of endogenous hormone levels in mosses are likely to be fruitful.
Prof. D. J. COVE (Department of Genetics, University of Leeds): “Genetic studies on the roles of auxins and cytokinins in the development of Physcomitrella patens.”
Observations of wild-type and mutant strains of P. patens lead to the following conclusions:
|1) Auxins are required for the transition of primary chloronemata (the first cell type to be produced on spore germination or tissue regeneration) to caulonemata.||a) Auxin non-synthesising mutants produce no normal caulonemata.
b) Drip feeding (the supply of a steady stream of fresh medium) of wild-type cultures produces only chloronemata. If auxin is added to the drip-feed medium, caulonema production is restored.
|2) Auxins depress the proliferation of primary and secondary chloronemata (cells morphologically similar to primary chloronemata but arising as side branches on caulonemata) but only in the presence of cytokinins||a) Direct observation of the effects of auxins on the wild-type.
b) Auxin non-synthesising mutants produce more chloronemata than wild-type.
c) Cytokinin non-synthesising mutants insensitive to auxins.
|3) High auxin concentrations interfere with gametophore development and enhance rhizoid production.||a) Direct observation of the effects of auxins on the wild-type.|
|4) Cytokinins play no major developmental role until caulonemal side branches have been initiated.||a) Cytokinin non-synthesising mutants develop normally to this stage.
b) The addition of cytokinins to drip-feed medium has no effect unless caulonemata production has been induced by the supply of auxin.
|5) Cytokinins are required for caulonemal side branches to develop into buds. High cytokinin concentrations both lead to every side branch forming a bud and block further gametophore development.||a) Cytokinin non-synthesising mutants produce no buds or gametophores.
b) Direct observation of the effects of cytokinins on wild-type cultures.
|6) Cytokinins depress chloronemal proliferation but only in the presence of auxin.||a) Cytokinin non-synthesising mutants produce more chloronemata than wild-type.
b) Direct observation of the effects of cytokinin on the wild-type.
c) Auxin non-synthesising mutants insensitive to cytokinins.
The A. G. M. was held after tea. Members later enjoyed a reception which had been generously provided by the Vice-Chancellor and kindly arranged by Prof. J. Colhoun, who deputized for the Vice-Chancellor on the day. Demonstrations on display during the evening conversazione included the following:
Dr. K. J. Adams: Some acquisitions of the B. B. S. library.
Dr. H.L.K. Whitehouse: Tortula stanfordensis in Britain.
After a day of sunshine, the Sunday dawned distinctly damp but began to clear up before the first field locality was reached, obviously with bryologists in mind. Our first stop was to the north of Heywood where members explored part of the Cheesden Brook valley. The area is one of varied habitats including woodland, rocks in the stream, wet outcropping gritstones, heath and unstable wet clay. Among the species seen were Atrichum crispum, Seligeria recurvata c.fr., Dicranella subulata (recently recorded in v.c. 59 for the first time this century), Gymnostomum aeruginosum c.fr., Discelium nudum c.fr. and Heterocladium heteropterum. The best discovery, however, was undoubtedly Mark Hill’s new county record of Fissidens curnowii.
A leisurely picnic lunch above Wardle prepared us for an onslaught on bryophytes in the vicinity of Watergrove reservoir, which we visited by permission of the North West Water Authority. There, we found Nardia compressa, Atrichum crispum, Oligotrichum hercynicum, Tetrodontium brownianum c.fr. and plentiful Discelium nudum c.fr., all species that are so typical of the Lancashire hills and, indeed, of similar parts of Yorkshire, as shown by the list compiled by two members returning home to that county. While most of us were ranging widely to see these plants, some concentrated on the exposed banks of the reservoir itself, to be rewarded by interesting discoveries of Fossombronia wondraczekii, Archidium alternifolium and Pohlia camptotrachela. It was there, also, that Alan Crundwell in finding Atrichum tenellum and Bryum tenuisetum made two further records for v.c. 59. One member seemed oblivious of time at this point but, once collected, we all went on to pay homage to an exceptionally fine population of Schistostega pennata in the vicinity of Brushes Clough reservoir above Crompton, arriving just as the moss was highlighted by the late afternoon sun.
I think it is true to say that this was an enjoyable meeting. For helping to make it so, the Society and I are indebted to Dr. J.N. Hartshorne and Mr. R. Wilson, the warden and administrator of Hulme Hall, for considering our needs so well and, above all, for their tolerance of late bookings and changed plans. My thanks are also due to Prof. Colhoun, whose assistance in organizing the reception I greatly appreciate, and to all those members who kindly sent lists of species seen during the field excursion.