A week-end meeting was held on 23 and 24 October in the Botany Department, University of Nottingham, by kind permission of Prof. C. G. C. Chesters.
About thirty-five members and guests attended the paper-reading sessions on the Saturday. The President, Dr. E. V. Watson, introduced the speakers and summaries of the papers are given below.
Dr R. E. Longton: ‘Some problems concerning the fertility of bryophytes.’
Field studies showed that sporophytes of the dioecious moss Pleurozium schreberi are rare over southern Britain, but widespread in northern Scotland and parts of southern Scandinavia, which form a zone towards the centre of the species’ latitudinal range. The rarity of capsules in southern Britain and some areas abroad was attributed to a corresponding rarity of male inflorescences, as bisexual specimens were collected in most fruiting localities, but only perichaetia were normally present elsewhere. Sporophyte development was stimulated experimentally by transplanting male plants into female colonies, but six non-fruiting bisexual localities were recorded in East Anglia. Under controlled conditions the rates of spore germination and vegetative growth increased with temperature independently of photoperiod between 5° and 20°C. The growth rates of male and female plants were similar, however, and there was no evidence that a narrower range of environmental conditions is necessary to stimulate perigonial than perichaetial initiation. It was thus not determined whether the rarity of male inflorescences results from a corresponding rarity of male plants or from failure in perigonial production. The former explanation was considered more likely, however, as perigonia developed during four successive years on male plants transplanted from East Anglia to the Wyre Forest, where male inflorescences were not recorded in natural populations. Preliminary results suggested a greater frequency of perichaetia than perigonia in four other species of dioecious moss rarely fruiting in Britain.
Miss M. L. Bowering: ‘Variation in Philonotis.’
The taxonomic problems posed by the genus were briefly considered and an account of the work carried out on Philonotis fontana, P. calcarea and P. seriata was given. It was shown that for a number of diagnostic characters there is no intergradation between the three species and growth under controlled environmental conditions confirmed that they are distinct. The results of investigations on the intra-specific variation of P. fontana were presented. It was found that P. fontana var. tomentella shows distinctive characters which it retains under various culture conditions and it was suggested that this variety merits ‘species’ status. The other varieties show a wide and continuously variable range of form but become indistinguishable when grown under similar environmental conditions. This indicates that the differences do not have a genetical basis.
Mr A.J. Harrington: ‘The Ecology and Culture of Scapania aspera and Scapania gracilis.’
The distribution and habitats of S. aspera and S. gracilis were reviewed and attention drawn to the relative importance of climatic and biotic factors. Experimental studies concerned with the germination and early development of spores and gemmae in sterile culture were reported.
In a dilute nutrient solution spores and gemmae of S. aspera failed to germinate in the absence of calcium, and spore germination was significantly reduced at a calcium concentration of 10 mg./l. Calcium was not required for the germination of S. gracilis spores and had no inhibitory effect at concentrations between 10 and 160 mg./l. At 200 mg./l. a significant reduction in percentage germination was observed. The subsequent differentiation and growth of S. gracilis sporelings were seriously affected by calcium concentrations exceeding 40 mg./l. and at concentrations of 100-200 mg./l. a large percentage of the sporelings failed to survive. Magnesium was shown to be less toxic over the same range and it is of interest that soils from S. gracilis sites were found to contain comparatively high levels of exchangeable magnesium.
It was suggested that the distribution of these species could be partially explained by the response of their propagules to available calcium.
Dr B. H. Green: ‘Sphagnum species as ecological indicators.’
Field and laboratory measurement and experiment suggest that Sphagnum spp. have well-defined ecological tolerance ranges and can serve as useful ecological indicators. Quantitative description of ecad variation can also enable estimates of habitat variables to be made from plant material. Sphagnum remains are frequently well preserved in peat deposits and both techniques find important application in the elucidation of past environmental conditions.
Habitat water analyses from S. recurvum and S. pulchrum sites together with culture experiments indicate that S. pulchrum has a greater requirement for sodium than S. recurvum. This may account for its largely maritime distribution. S. imbricatum forms ecads in relation to the water level under which it grows. Measurements of branch density and branch length show direct and inverse relationships respectively with the depth of the water level. Measures of subfossil material indicate that the plant grew under higher water levels in the past than in most of its stations today.
Estimates of the relative abundance of species of the Cuspidata and Acutifolia sections over the mire surface in the past have been made from leaf counts of horizons of peat profiles of Wybunbury Moss, Cheshire. Aquatic Cuspidata dominate during wet Post-glacial epochs and terrestrial Acutifolia in dry.
Dr D. H. Dalby: ‘Photography as an aid in the study and identification of bryophytes.’
By means of black and white and colour transparencies some of the main bryological applications of photography were discussed, particular emphasis being placed on those situations where photographs are more suitable than drawings. This may be, for example, when there are overriding demands for authenticity, accuracy or speed. Certain features such as leaf areolation and the spatial interrelation of parts of plants lend themselves particularly to photographic treatment.
General discussion followed the last paper. The President thanked the speakers, Dr J. H. Dickson who had arranged the paper reading, and members of the Botany Department who had given assistance.
The evening soirée was also held in the Botany Department, members being the guests of the Department. The exhibits displayed were as follows:
|Dr R. E. LONGTON:||Fairy rings in Antarctic mosses.|
|Dr D. H. DALBY:||Photographs to demonstrate cell form in the leaves of Hypnum cupressiforme var. resupinatum, Pylaisia polyantha and Platygyrium repens. Habit and leaf structure in Fissidens celticus.|
|Dr J. H. DICKSON:||(a) Fossil bryophytes of the Quaternary in Britain.
(b) Bryophytes of Wicken Fen.
|Mr E. C. WALLACE:||Photographs of bryologists from the album founded by the late secretary Mr A. Thompson.|
|Mrs J. A. PATON:||Bryophyte herbaria.|
There was also a display of:
(a) old books illustrating early distribution of bryophytes in Ireland (Mr R. D. Fitzgerald),
(b) early British and continental books on bryophytes (Mr A. D. Banwell and Miss D. Bexon).
About twenty-five members and friends undertook the excursion to Monk’s Dale, Derbyshire, on Sunday 24th, being favoured by a fine clear day in contrast to the fog which had hampered movement on Saturday. The Dale yielded a rich collection of calcicolous bryophytes, over 100 species being found, among which may be noted Gymnostomum calcareum, Plagiobryum zieri, Seligeria doniana, Trichostomum brachydontium var. cophocarpum, Pottia bryoides (in fruit), Barbula revoluta (in fruit), Rhynchostegiella tenella, Amblystegiella sprucei, Nowellia curvifolia, Scapania aspera, Solenostoma sphaerocarpoideum and Leiocolea muelleri.