A week-end meeting was held on 25-26 October in the Department of Biological Sciences, University of Aston in Birmingham, by kind permission of Professor A. J. Matty. The President, Mr J. H. G. Peterken, took the chair on Saturday, and the following papers were read, summaries of which are given below.
Mr T. J. Bines: ‘Aspects of growth and nutrition of Ulota crispa.’
Ulota crispa (Hedw.) Brid. was found to be limited in its colonization to rugosities in bark. An accumulation of water was detected at these points using a dye technique. On examination of these sites on bark of Corylus avellana, Sorbus aucuparia and Quercus sp. there was no detectable difference in major cation content between these sites and the plain bark. The growth rate of cushions in relation to the twig diameter was measured. A positive correlation was obtained between the log. of twig diameter and the age of the cushion. It was found that the nutrient content of small cushions was high. This corresponded to a period of rapid increase in length and width but not in height. After this rapid increase the nutrient level of the cushion remained constant on a µg./g. dry wt. basis. Cushions do not therefore accumulate nutrients with age but maintain the same level after the initial growth increase, at least until they are colonized by other species. Further analyses of bark nutrient contents have been carried out. An interesting correlation was obtained between the potassium and magnesium levels (+ve) and the phosphate and iron levels (-ve). This probably indicates dust contamination of the bark surface. Leaching rates from the bark surface and Ulota crispa cushions were assessed. Little loss of the major cation occurred from the moss but measurable amounts, providing a weak nutrient solution for growth of epiphytes, were leached from bark.
Mr W. J. Syratt: ‘The effect of sulphur dioxide on epiphytic bryophytes.’
A continuous flow capillary dilution and humidifying assembly has been employed to investigate the effects of low concentrations of SO2 (down to 1 p.p.m.) at known humidities on chlorophyll breakdown, respiration rate and sulphate accumulation in seven epiphytic bryophytes. Results have shown that chlorophyll degradation is dependent both on the concentration and humidity at which the gas is supplied, the higher the humidity the greater the breakdown. Dicranoweisia cirrata had least breakdown. The SO2 tolerant moss D. cirrata was shown to be capable of converting SO2 to SO4¯ with a higher efficiency than the other species investigated and that this capability is light-dependent. Metzgeria furcata, a tolerant liverwort, though capable of large sulphate accumulations, was shown not to be more efficient than other more sensitive species. The more sensitive species converted only small amounts of SO2 to SO4¯. The fact that D. cirrata accumulates SO4¯ in the field has been demonstrated by means of a 160 km. transect north-east from London. As the distance from London increased (and hence SO2 pollution decreased) so the extractable sulphate in the moss decreased. The use of epiphytic bryophytes as indicators of air pollution, based on the sensitivity of the species investigated experimentally using fumigations with SO2 and on their observed field distribution, was considered possible. A range of tolerances and/or sensitivities was found in the species investigated, D. cirrata being most tolerant and Ulota crispa being most sensitive.
Dr P. J. Grubb: ‘The growth of the sporophyte of Polytrichum formosum Hedw.’
Whereas Haberlandt’s early work on sporophyte growth suggested an emerging independence from the gametophyte, Rastorfer’s studies suggested a continuing strong dependence for photosynthate. Experiments on defoliation and covering of the gametophyte in Polytrichum supported Rastorfer’s view. So did experiments on the growth of isolated sporophytes – they develop a great deal but their dry weight decreases. Recent studies by Paolillo and Bazzaz confirm a real difference in this respect between Funaria (Haberlandt’s plant) and Polytrichum (Grubb’s and Rastorfer’s). Covering the sporophyte of Polytrichum at various stages discloses a morphogenetic requirement for light. Long exposures are needed for normal development. Red light is most effective. Infra-red light does not reverse the red effect. The sources of the organic supplies to the sporophyte seem to vary: at least sometimes net redistribution from older organs is important as well as current photosynthesis in the gametophyte leaves.
Dr M. C. F. Proctor and Mr H. M. Hinshiri. ‘Some experiments on assimilation by bryophytes following desiccation.’
After a period of desiccation bryophytes regain their normal rate of net assimilation only after an ‘activation period’. In experiments with Anomodon viticulosus, Porella platyphylla and other species, using a Warburg apparatus, it was shown that this effect is due to enhanced respiration, more or less proportionate to the duration and intensity of the preceding desiccation. There were also indications of increased sensitivity to stimulation of respiration by handling during recovery from desiccation. For moderate periods of desiccation there is apparently little effect on the photosynthetic mechanism, though there are indications that this is affected by prolonged desiccation. The conclusions agree broadly with those of Willis (with Tortula ruraliformis) and Ensgraber (with Conocephalum conicum), but the respiration peaks were of shorter duration, comparable in length with the ‘activation periods’ indicated for Hylocomium splendens by Stålfelt.
Dr R. S. Clymo: ‘The growth of Sphagnum.’
The substance of this paper is to be published in the Journal of Ecology, vol. 58, 1970.
Mr K. Lewis: ‘Experimental taxonomy of the bulbilliferous Pohlia.’
The bulbilliferous Pohlia are characterized by the production of bulbils or gemmae in the axils of their leaves. The bulbils differ both in form and in the number produced per leaf axil. These differences have been used as diagnostic features to delimit the taxa within the group. However, many of the descriptions and illustrations of bulbils in the literature are ambiguous and misleading and have caused much misidentification. Further, there has been some speculation concerning the stability of the buibils, regarding both their form and number per axil. For these reasons, the nomenclature and taxonomy of the bulbilliferous Pohlia has become a confused issue. Samples of these plants, collected from all over the British Isles, have been subjected to culture under uniform environmental conditions and it has been possible to resolve the limits of variation within each taxon. The Census Catologue of British Mosses (Warburg, 1963) lists six bulbilliferous species, namely Pohlia annotina (including the var. decipiens), P. proligera, P. bulbifera, P. rothii, P. drummondii and P. gracilis. As a result of the present work, it is proposed to merge P. annotina, P. annotina var. decipiens and P. proligera in one taxon, and two new taxa will be created.
After discussion and questions to speakers, the President thanked all who had contributed and Dr R. E. Longton for arranging the programme of papers.
|In the evening a conversazione was held at the University and the following exhibits were displayed :|
|Mr T. LAFLIN:||Bryophyte flora of Warwickshire.|
|Dr M. E. NEWTON:||Sex chromosomes in bryophytes.|
|Mr M. V. FLETCHER:||Some bryophytes from Skye.|
|Dr J. G. HUGHES:||Aspects of growth in Phascum cuspidatum.|
|Mr E. C. WALLACE:||Portraits of bryologists.|
|Mr K. LEWIS:||Bulbilliferous Pohlia.|
About twenty-five members, including the President, met on Sunday morning at Banners Gate, Sutton Park (v.-c. 38). The party walked first to Long Moor Mill Pool, where Pellia neesiana* and Mnium rugicum* were found. A number of uncommon Warwickshire bryophytes were refound in the boggy areas of Long Moor, including Splachnum ampullaceum, Mnium pseudopunctatum, Cratoneuron commutatum and its var. falcatum, Drepanocladus exannulatus, D. revolvens var. intermedius and Acrocladium giganteum.
[* new vice-county record]
On wet peat by a ditch near Rowton’s Well Pohlia bulbifera* was found, confirming earlier gatherings, the identity of which had been doubted, from this place. Also on peaty ditch sides were Calypogeia muelleriana and Dicranella cerviculata. Members then moved on to Little Bracebridge bog and pool, where a number of interesting plants were refound. Among these were Leiocolea bantriensis, Scapania irrigua, Sphagnum plumulosum, Fissidens adianthoides, Mnium seligeri and Drepanocladus vernicosus. Mrs Appleyard discovered also Sphagnum teres, recorded by Bagnall in the nineteenth century from three places in Sutton Park, but recently found in v.-c. 38 only by Coleshill Pool. A picnic lunch was eaten in the Park, made enjoyable by the good weather.
A smaller number of people went on to the Alvecote Pools Nature Reserve, where they were received by Mr G. A. Arnold, the Warden. The reserve is on the site of a disused colliery, Subsidences have filled with water, forming large pools and boggy areas. Riccardia sinuata, R. pinguis, Lophocolea cuspidata and Dicranella cerviculata were found at the pool margins. Members were interested in the large slag heap which is erratically burning inside after spontaneous combustion. Where the burning comes near to the surface the heat kills the vegetation over areas of variable size, and the hot, bare ground is colonized by Pohlia nutans and Campylopus introflexus. Sulphur dioxide produced by the burning appears to have no ill effect on these two species. On bare wet ground at the base of the slag heap were Cephaloziella starkei, Lophozia bicrenata, Leptobryum pyriforme and the small-bulbilled form of Bryum bicolor. The party dispersed after thanking Mr Arnold for conducting them round the area.
J. G. Hughes