The autumn meeting was held on the weekend of 2 and 3 October in the Botany School of Cambridge University, by kind permission of Professor P. W. Brian, F. R. S. Some forty-five members attended on the Saturday when the President introduced six speakers, summaries of whose papers are given below.
Dr D. Briggs: ‘Heavy metal tolerance in bryophytes’.
Large amounts of lead and other heavy metals are released by some industrial processes and it is known that these metals accumulate in soils and vegetation downwind of industrial areas. There is also published evidence that similar accumulation takes place at roadsides. Very little is known, however, about lead pollution of plants and soils in cities, although the number of possible sources of lead pollution in urban areas suggests that high levels of lead might occur.
An investigation of Marchantia polymorpha in western Scotland has revealed high levels of lead in city populations (e.g. 5333 ppm dry weight at St Enoch Square, Glasgow) and in populations remote from towns but near main roads (e.g. 7792 ppm dry weight by the Glasgow-Carlisle Road near Beattock) while lower levels are often recorded in country districts relatively remote from traffic (e.g. 149 ppm dry weight at a disused paper mill, Milngavie). Similar results have been obtained with Bryum argenteum and Funaria hygrometrica.
A study of lead tolerance has been carried out with several Marchantia populations. On the basis of gemma growth on agar containing lead, evidence has been found that city populations are much more tolerant of lead than those found growing in relatively uncontaminated country districts.
Dr H. J. B. Birks: ‘Some aspects of the bryophyte flora of Skye’.
The bryophyte flora of Skye, the largest island of the Inner Hebrides consists at present of 372 mosses and 182 hepatics. The flora is extremely diverse, both ecologically and phytogeographically and this has been correlated with the varied geology, topography and climate of the island. The phytogeographical affinities of the flora are broadly similar to those of the phanerogam flora with a predominance of Atlantic, sub-Atlantic. Continental-Northern, Northern-Montane and Arctic-Alpine elements. The flora is remarkable for the large number of southern Atlantic species growing at or near their northern limits on Skye, for example Acrobolbus wilsonii, Adelanthus decipiens, Jubula hutchinsiae, Lejeunea mandonii, Marchesinia mackaii, Radula carringtonii, Sematophyllum novae-caesareae, the pteridophyte Hymenophyllum tunbridgense and the lichen Sticta canariensis.
Variations in the distribution patterns within Skye are related to climatic variables and to geological differences: there are several species restricted on Skye to limestone rocks and to basalt or gabbro, whereas several occur on a wide variety of basic substrata.
The role that bryophytes play in the vegetation of Skye is shown by their phytosociological importance in the characterization of Associations within the Oxycocco-Sphagnetea Br.-BI. & R. Tx. 1943 and the Scheuchzerio-Caricetea fuscae (Nordhagen 1936) R. Tx. 1937. Each alliance within these classes has a distinctive bryophyte assemblage, for example alliance Eriophoron latifoliae Br.-BI. & R. Tx. 1943 is characterized on Skye by Campylium stellatum, Cinclidium stygium, Drepanocladus revolvens, Fissidens adianthoides, Riccardia pinguis and Scorpidium scorpioides.
Mr N. J. Collins: ‘Bryophyte growth and productivity in the Antarctic’.
On Signy Island some ground is free of snow and ice for 3-4 months of each year and extensive communities of bryophytes and lichens have developed. Cushions of Andreaea and Grimmia species occur in the drier, more exposed habitats with least winter snow cover, while carpets of Brachythecium, Calliergon and Drepanocladus species and hummocks of Brachythecium cf. subplicatum (Hamp.) Jaeg. and Bryum algens Card. occur in habitats with the greatest winter snow depths and with melt water available throughout the summer. The turf-forming species Polytrichum alpestre and Chorisodontium aciphyllum (Hook. f. & Wils.) Broth, have produced extensive semi-ombrogenous peat banks. With the exception of C. aciphyllum, all these species show a periodicity of growth which is marked by morphological features.
Production varies both between and within species, even over short distances. Stems of cushion forming species grow up to 0·5 cm in a season, but large cushions are rare, so turnover must be rapid. This length increment is similar to that of moss turfs where production is between 300 and 500 g/m2/season. Carpets and hurnmocks exhibit the highest production. attaining some 900 g/m2/season, corresponding to length increments of 3-4 cm. There is. however, little build up of peat. so either breakdown and physical removal are rapid, or the carpets are of recent origin. In contrast, the peat banks grow more slowly but decomposition is negligible. Once these banks come to lie above the winter snow as a result of moss growth or of climatic change, they are eroded or become encrusted with lichens.
At the present time the annual melt is becoming progressively greater and freed surfaces are colonized by carpets. The initially abundant water supply is restricted as the carpets are colonized by turf-forming species and also as the melt occurs more rapidly and earlier in the summer. Cyclic changes result in cycles of growth of bryophytes, lichen encrustation and or erosion, interspersed with continuous snow cover.
Professor S. Inoue: ‘B-chromosomes in Lesquereuxia robusta Lindb. ‘.
Populations of L. robusta from central and southern Japan have been studied cytologically. The chromosome number (n=11) and karyotype reported in the literature were confirmed for most of the samples examined, but in some cases abnormal karyotypes were found. The abnormalities involved the addition of between one and four chromosomes to the normal complement, such chromosomes being either metacentric or telocentric, but always smaller than the m-chromosomes of normal cells. Another distinction between the extra chromosomes and m-chromosomes was that the latter were heteropycnotic in the interphase nucleus (they have therefore been designated m(h)-chromosomes).
As a result of these observations it was proposed that the additional chromosomes could be described as B-chromosomes even in an investigation of somatic cells. Further studies of the meiotic behaviour of these chromosomes would be most useful.
Dr J. G. Duckett: ‘Spermatogenesis in bryophytes’.
The contribution made by the electron microscope towards our understanding of the male gamete of bryophytes was reviewed. New observations on spermatogenesis in Anthoceros laevis were compared with published reports on the fine structure of moss and liverwort spermatozoids.
The plastids of Anthoceros undergo a remarkable series of changes during spermatogenesis. In contrast to those of normal vegetative cells, the plastids in early generations of spermatogenous cells lack pyrenoids and have few internal lamellae. Plastid division is in step with mitosis in the spermatogenous cells, so each spermatocyte has one plastid. With successive mitoses the plastids become progressively smaller until those in the young spermatocytes are ovoid structures 1-2 µm in diameter (cf. over 10 µm long in vegetative cells), indistinguishable from the spermatocyte plastids of mosses and liverworts. Metamorphosis of the spermatocyte involves precise and highly co-ordinated organelle differentiation and re-arrangement. In the young spermatocytes the two flagellar basal bodies with the underlying microtubular band and lamellar layers of the multilayered structure (MLS) lie as an integrated unit at the periphery of the cell. This is equivalent to the blepharoplast of light microscopists. The nucleus migrates into contact with them and forms an anterior projection. Elongation of the nucleus then begins and the microtubular band progressively extends beyond the lamellar layers of the MLS around its outer surface. Beneath the lamellar layers at the anterior tip of the nucleus lies a complex mitochondrion, the apical body. Within the concavity of the elongating nucleus lies the limosphere: the spermatocyte plastid surrounded by a mitochondrial sheath. As nuclear elongation continues the clearly defined partitions of the lamellae of the MLS become occluded and the limosphere migrates to the posterior tip of the nucleus. In mature spermatozoids the chromatin in the sinistrally-coiled rod-like nucleus is completely condensed and the lamellar layers of the MLS are absent. The microtubular band forms the skeleton of the motile gamete in the absence of a cell wall. The plastid contains large amounts of starch. Since there is no evidence that this is utilized as an energy source during periods of prolonged motility it was suggested that the amyloplasts enable the motile gametes to respond to gravitational forces.
Dr A. D. Horrill: ‘Some aspects of the conservation of bryophytes’.
Conservation of the British bryophyte flora must fulfill two objectives: protection of rare species and preservation of habitats where bryophytes form an important component of the vegetation. In Great Britain there is a considerable number of species dependent on an oceanic climate and these are particularly valuable subjects for research into climatic change with respect to both geography and time.
Excluding climatic change, the dangers to the bryophyte flora are all of human origin, either by deliberate collecting or as an incidental consequence of other activities. Air pollution, land drainage, urban development, felling and replanting of native woodlands and public pressure on areas such as sand dunes all reduce bryological variety. Collecting for horticultural purposes is a practice more unsightly than dangerous, but rare species may easily be gathered with common plants. Selective collection by bryologists is more dangerous as it is often concentrated on well-known localities, so the building up of extensive private herbaria is surely to be deplored when large public herbaria are available. Photography might well take the place of collecting for a large number of the more readily identified species.
Bryologists could do much to help by using their specialized knowledge to advise conservation organizations on the designation of important sites and by providing information on the environmental needs and distribution patterns of the rarer species.
After discussion the President brought the session to a close by thanking the speakers and also Dr H. L. K. Whitehouse and Dr H. J. B. Birks who had acted as local secretaries for the meeting.
|In the evening members reassembled in the Botany School for a conversazione at which the following exhibits were presented:|
|Dr A. J. E. SMITH:||‘B. B. S. Distribution Maps Scheme’.|
|Mrs M. R. SMITH:||‘Drawings of British mosses’.|
|Mr. M. V. FLETCHER:||‘Some mosses in cultivation’.|
|Mr R. J. PANKHURST:||‘Computer-generated keys: Barbula in Cambridgeshire’.|
|Dr R. A. FINCH:||‘Tortula cf. freibergii Dixon & Loeske from St Leonards and Fairlight Glen. Hastings’.|
|Dr H. L. K. WHITEHOUSE:||‘Tortula stanfordensis Steere with mature capsules’.|
|‘Two undescribed species of Dicranella.|
Field meeting to Bradfield Woods, Bury St. Edmonds
On 3 October Dr O. Rackham led members into the Bradfield Woods nature reserve near Bury St Edmunds. Suffolk (v.-c. 26). This reserve comprises Felsham Hall Wood and part of the adjoining Monks’ Park Wood. Recent finds in Felsham Hall Wood have included Plagiochila aspleniodes var. major, Lejeunea cavifolia, Sphagnum subsecundum var. auriculatum, Isopterygium seligeri and Plagiothecium latebricola. The Plagiochila and the Plagiothecium were refound, and other species seen included Calypogeia arguta* in a shaded ditch, Sphagnum subsecundum var. inundatum in damp hollows. Bryum ruderale* on a path. Tetraphis pellucida on stumps and Plagiothecium curvifolium* at tree bases. In arable fields near the wood Sphaerocarpos sp., Riccia glauca, R. sorocarpa, Ditrichum cylindricum*, Dicranella schreberana, D. staphylina, Physcomitrella patens, Ephemerum serratum var. minutissimum*, Bryum klinggraeffii* and B. violaceum* were found. Subsequently, some members stopped near Fornham St Martin just north of Bury St Edmunds, where Physcomitrella patens. B. klinggraeffii and B. violaceum were found in arable fields, Barbula trifaria and Bryum radiculosum* on a bridge and Eurhynchium megapolitanum amongst grass. Some members saw Ricciocarpus natans in a ditch at Wicken Fen (v.-c. 29).
[* New vice-county record.]
G. C. S. Clarke