This year’s autumn meeting, which was held in the Department of Botany at Imperial College. London, by kind permission of Professor A. J. Rutter. was the best attended meeting the society has yet held with over sixty members present. On the first day (Saturday 28 October) the President introduced six speakers and summaries of their papers are given below.
Mr P. Pitkin, Commonwealth Forestry Institute, University of Oxford: ‘Environmental factors and growth in corticolous bryophytes’.
Culture experiments have shown that bark and water chemistry are important in determining tree preferences and ecological distribution of corticolous bryophytes. The behaviour of Cryphaea heteromalla, Hypnum cupressiforme and Lophocolea heterophylla in sand culture with water extracts of different barks corresponds closely to that in the field. Growth on bark extracts from different heights on a trunk indicates that there may be a growth inhibitor in the bark higher up the trunk to which L. heterophylla seems particularly sensitive. Growth on bark extracts also showed that stem-flow water is an important source of nutrients.
When bark extracts were amended with mineral acid and alkali C. heteromalla and H. cupressiforme were more sensitive to pH than L. heterophylla. Amendment of various bark extracts to the same pH altered their relative suitability for growth. Sensitivity of C. heteromalla and H. cupressiforme was further demonstrated by their growth on artificial culture media. Optimum pH for the growth of these species was 6-6-5 but Isothecium myosuroides showed maximum growth at pH 7. Above pH 5 growth of H. cupressiforme exceeds that of I. myosuroides but in more acid conditions the rates are reversed. Since these species have similar growth forms and occupy similar habitats this may be an important factor in competition between them.
Variations in the pH of oak bark in England and Wales, which have been correlated with atmospheric pollution and rainfall, may be important in restricting the geographical distribution of corticolous bryophytes. Near Oxford the pH of oak bark is about 3-6 and culture experiments show that this is so acid that growth is minimal.
Gemmae of Ulota phyllantha will germinate on discs of oak bark cut from the foot of the trunk beneath epiphyte cover, but they die on discs of uncolonized bark from higher up the trunk suggesting the presence of possible growth inhibitors. Washing seems to remove these from the bark. The effect of tannic acid and Calluna tannin on early stages in the development of H. cupressiforme and U. crispa was studied. Spore germination was unaffected by tannin concentration, but there was a marked effect on the development of sporelings, although U. crispa was considerably more sensitive than H. cupressiforme. This difference is reflected in the ecology of the two species: H. cupressiforme growing on trunks has more tannin in its water supply than U. crispa which grows on twigs.
Professor W. W. Schwabe, Department of Horticulture. Wye College: ‘Growth regulation in Lunularia cruciata and the role of lunularic acid in lower plants’.
The Mediterranean strain of L. cruciata (Israel material) is sensitive to photoperiod in its growth: it becomes dormant in long day conditions. Dormant thalli exhibit considerable drought resistance and may be kept for a number of years in the air-dry state, while actively growing thalli in short days are rapidly killed by dry conditions. There is no sharply defined critical day length for dormancy induction and at higher temperatures relatively shorter day lengths induce cessation of growth. A few short day cycles suffice for growth resumption.
Gemmae require light for ‘germination’ but will survive for months in total darkness. Both dormancy induction by long days and germination of gemmae are phytochrome controlled in a complex manner involving interactions with temperature. Drastic changes in response to red or far-red light, given in the middle or at the end of the photoperiod. or in the dark period, suggest the involvement of internal rhythms.
The natural growth substances of higher plants (auxins and gibberellins) appear to have little or no promoting effects on the growth of Lunularia and become inhibitory at higher concentrations, as does abscisic acid. However, chelating substances (EDTA) promote growth.
It has been shown that dormancy of thalli and of gemmae in the gemma cup is controlled by the level of a natural growth inhibitor recently isolated and structurally identified (lunularic acid). This substance has since been found in all species of liverwort and algae so far examined, but appears to be absent from mosses, ferns and higher plants. In Lunularia it is quantitatively controlled by photoperiod. It also acts as an inhibitor of algal growth and germination of fungal spores. It delays seed germination in some higher plants.
Dr A. R. Sheldrake, Department of Biochemistry, University of Cambridge: ‘Auxin and bryophytes’.
Auxin production in higher plants has for many years been thought to take place in meristematic cells, but it now seems probable that it is normally produced as a consequence of cell death, the auxin production of meristematic regions being attributed either to the presence of regressing nutritive tissues (as in embryo, seed and pollen development) or to differentiating vascular tissue: xylem cells die as they differentiate. Attempts to explain the growth of non-vascular plants in terms of auxin production by meristematic cells by analogy with higher plants are therefore misleading and a critical examination of the evidence for the involvement of auxin in, for example, apical dominance in bryophytes and fern gametophytes reveals that it is unconvincing. Nor is there any persuasive evidence that these plants normally produce auxin.
There is, however, one positive response of liverworts to auxin which occurs at low concentrations and which may be of physiological significance’ the induction of rhizoids. The response to exogenous auxin could take place under normal growth conditions if auxin is present in the environment. Substrata on which bryophytes were growing were analysed and found to contain amounts of auxin sufficient to induce rhizoids; similar concentrations of auxin were also found in humus-rich soil on which no bryophytes were growing.
This response to environmental auxin, produced during the decomposition of organic matter by soil micro-organisms, may be of adaptive importance in that rhizoids will be induced in regions where nutrients are released. The induction of buds on moss protonemata by low concentrations of cytokinins could perhaps also be a response to environmental cytokinin released from RNA in decomposing organic matter.
Dr D. W. Shimwell, Department of Geography, University of Manchester: ‘The ecology of moss-dominated vegetation on the heavy metal mine spoil heaps of the Southern Pennines’.
Moss dominated communities are rare on the heavy metal mine spoil heaps of the Southern Pennines and are more or less restricted to areas where the spoil overlies impervious shale and where the habitats are thus suitably moist. Three ecological features are characteristic of these habitats—quantities of lead and zinc toxic to most phanerogams, low concentrations of nitrate, phosphate and potassium and the acidity (pH 4.3-5.2). In the Peak District and Grassington (Yorkshire) regions three species of moss—Dicranella varia, Bryum pseudotriquetrum and Philonotis fontana—are most commonly associated with such habitats, and analyses of tissues and soil samples indicate that lead and zinc concentrations are far greater than those previously reported for mosses. In periods of alternating drought and wetness, D. varia excretes and deposits a crust rich in heavy metals with recorded values of up to 6% Pb and 6000 ppm Zn. In contrast, living tissues contained up to 11,950 ppm Pb and 5985 ppm Zn. P. fontana shows a marked localization of both metals in older tissues (10,015 ppm Pb and 2420 ppm Zn maxima) with comparatively low values in actively growing tissues (to 423 ppm Pb and 297 ppm Zn). Other mosses showing a capacity for heavy metal absorption include Camptothecium lutescens and Encalypta vulgaris. Analyses of twenty samples of Fontinalis antipyretica from two rivers flowing through former lead mining areas indicate low values of both lead (0-10 ppm) and zinc (10-90 ppm).
Dr S. W. Greene, British Antarctic Survey, Botanical Section: ‘The International Association of Bryologists’.
The idea of forming an International Association of Bryologists, affiliated with the International Association of Plant Taxonomists (IAPT), was first discussed at the Pacific Science Congress in 1966 when a steering committee was appointed to report to the next International Botanical Congress of the feasibility and aims of such an association. The formation of the Association was formally proposed and passed by the general assembly of the International Union of Biological Sciences at the Congress in Seattle, 1969. Affiliation with IAPT ensures financial and secretarial support for the Association and the possibility of using its outlets for publication, e.g. Taxon, for a regular Bulletin of Bryology and Regnum Vegetabile for larger specialist works. The first Bulletin of Bryology appeared in Taxon 21 (2/3), 375-6. in May 1972.
The aims of the Association are to promole the study of all aspects of bryology throughout the world by such means as the organization of meetings and symposia, the production of regular news bulletins, special purpose reports and publications, e.g. a periodic list of all new taxa and combinations, an index of types, a detailed register of bryological collections and their locations, etc. Two current projects are a directory of bryologists and their research projects and a conspectus of bryological taxonomic literature, the latter being intended as an introduction to the bryophyte floras of the world arranged on a regional basis.
DR D. H. Dalby, Department Of Botany, Imperial College: ‘The BBS in the 1970s’.
The present-day activities of the British Bryological Society can be traced back to its origins as the Moss Exchange Club, which by encouraging comprehensive collecting (in spite of the very high standards of identification attained) did appreciable harm to bryology as a reputable study in Britain.
The major works of bryologists such as Dixon and Macvicar formed a transition to the period of better understanding of the causes of variation of species in nature, with an awareness of the effects of environmental factors. At the same time, the Society has responded to the developing needs of a body combining fieldwork with research, both by amateur and professional members. The question arises as to whether the Society’s present activities are adequate, and if they are not, should encouragement be given to a change in emphasis or to entirely new activities?
As a purely personal view, I would favour the following lines of development: 1, greater emphasis on the 10 km square recording and a playing down of the vice-county recording schemes; 2, active co-operation with the Nature Conservancy and other conservation bodies, with the possibility of holding field meetings in nature reserves for the purpose of recording and advising in management plans; 3, the organization of specialist symposia (in conjunction with other biological societies) on such subjects as the physiology of epiphytes, phyto-sociology of cryptogam-dominated communities, etc.; 4. increasing help given to beginners, both by way of reference material and by organizing field meetings where the objective is one of teaching methods of identification and ecological principles; 5, increased publicity for the Society with the objective of both adding to our membership and also improving the image of bryology as a scientific study in this country.
The Annual General Meeting was held at 7.30 p.m. and this was followed by a conversazione at which the following exhibits were presented:
|Mr S. G. HARRISON:||The Jackett bryophytes; a bound exsiccata.|
|Mr M. V. FLETCHER:||A collection of living New Zealand mosses.|
|Mr M. O. HILL:||An ordination of mosses based on vice-comital distribution.|
|Dr M. NEWTON:||Liverwort chromosomes.
Mosses common to Great Britain and to the sub-Antarctic zone.
|Mrs K. LEWIS:||Coal pollution effects on Eurhynchium riparioides.|
|Dr K. BENSON-EVANS, Mr M. GRIFFITHS,
Mrs K. LEWIS and Mr J. MORGAN:
|Regeneration studies in some mosses.|
On 29 October about twenty members attended a field meeting in Surrey (v.-c. 17) led by the President and Mr J. C. Gardiner. In the morning a visit was paid to part of Box Hill, and in the afternoon a boggy woodland area, a little to the north of Leith Hill, was explored. As might be expected from such well-worked areas only one new vice-county record was reported, but useful additions were made to the existing lists for the 10 km squares. Amongst the ‘specialities’ from Box Hill, Dicranum montanum, D. strictum, Isothecium striatulum, Thuidium hystricosum, T. philibertii, Tortula stanfordensis and Lejeunea lamacerina var azorica were seen, while additions to the square in the Leith Hill area included Dicranum strictum, Bryum bornholmense, B. violaceum, Pohlia lutescens*, Plagiothecium latebricola and Cryptothallus mirabilis.
[* New vice-county record]
The Society is grateful to the leaders of the field meeting and to Dr D. H. Dalby who acted as local secretary for the weekend.
G. C. S. Clarke