Dr E. F. Warburg and Mr A. J. E. Smith organized the meeting which took place on 29 and 30 October 1960, in the Botany Department of Oxford University (by kind permission of Prof. C. D. Darlington).
The President, Miss E. M. Lobley, was in the chair on the Saturday and forty-one members and visitors were present to hear the following papers:
Dr K. R. Lewis: ‘The genetics of Bryophytes’. This paper is printed on pp. 111 – 130.
Dr M. C. F. Proctor: ‘Epiphytic bryophyte communities in the Dartmoor oakwoods’.
The Dartmoor woods fall into two main groups: three small but well known woods (including Wistman’s Wood) on the granite plateau, above the 1000 feet contour, and receiving a rainfall of c. 60-70 inches a year; and a much more extensive and varied series of woods, mostly below the 1000 feet contour, in the deep river valleys cut into the granite and Culm Measures round the edge of the Moor.
In the driest valley woods, the tree bases are generally occupied by Isothecium myosuroides, with Mnium hornum, Dicranum scoparium, etc. This gives way above to a zone of Hypnum cupressiforme var. filiforme, with scattered Dicranum scoparium, and this in its turn to a zone rich in lichens, especially in well-lighted situations. The upper branches carry an open Ulota-Frullania dilatata community. The Ulota-Frullania community may persist on the trunks of coppice oaks until they reach a diameter of 25 cm. or so, and is then often somewhat richer in species, with Neckera pumila, Orthotrichum lyellii, O. striatum, etc. Hazel and ash bear similar Ulota-Frullania communities, though on ash the Ulotas tend to drop out of the later stages.
In the higher and wetter valleys the bases are still covered with I. myosuroides, often extending for a considerable distance up the trunk, but this gives way upwards to a community consisting largely of Frullania tamarisci and Isothecium myosuroides or Hypnum cupressiforme var. filiforme. Above this the upper branches are often covered with Hypnum cupressiforme var. filiforme, while the younger twigs bear the open Ulota-Frullania community.
In Wistman’s Wood and Black Tor Copse the trunks and larger branches are typically covered with a thick mat of Isothecium myosuroides, Dicranum scoparium, Scapania gracilis, etc. This shows indications of a cyclical succession, apparently building up from an open community of which Isothecium myosuroides, Plagiochila punctata and Douinia ovata are characteristic consituents, and which is persistent on the overhanging surfaces of trunks and branches. The upper branches are occupied by Hypnum cupressiforme var. filiforme and the common corticolous lichens ( Hypogymnia physodes, Parmelia spp. etc.), while the Ulota-Frullania dilatata community is usually confined to the highest twigs, and is rather poorly developed.
Transitions between the situation of Wistman’s Wood and that in the valley woods can be found in some woods on the granite in the higher parts of the valleys.
Mr P. J. Grubb: ‘The study of translocation in Bryophyta, using radio-active isotopes.’
An account was given of some experiments on Polytrichum spp. designed to investigate the processes involved in the translocation of mineral nutrients. It was concluded that nutrients are drawn up passively into the shoot in the transpiration stream; there is no evidence of an active redistribution such as occurs in the phloem of higher plants. The mineral supply to the sporophyte also appears to be passive, involving no special active absorption in the foot.
Prof. P. W. Richards: ‘ Campylopus introflexus and C. polytrichoides in the British Isles.’
- introflexus (Hedw.) Brit. and C. polytrichoides De Not. are regarded by Dixon and most other modern British bryologists as synonymous. Giacomini has, however, shown that they are well defined species with distinct distributions, the former being found mainly in Australia and the Americas, the latter in Europe, Africa and tropical Asia. C. introflexus was first found in Europe in 1954 by R. B. Pierrot and P. Stormer who recognized it independently in a locality in Finistère (France). No British record is known previous to 1941, but there is evidence that the species is spreading rapidly and occupying a much larger area than C. polytrichoides which is confined to South-west Ireland, North Wales, Pembrokeshire and south-west England and shows no signs of spreading.
- introflexus tends to occur on peat, often where it has been burnt or recently cut, while C. polytrichoides grows in rocky habitats. The hair point, short and more or less straight in C polytrichoides, long and usually abruptly recurved in C. introflexus, is an obvious difference between the two species. Dr E. F. Warburg kindly read the paper on behalf of Prof. Richards who, unfortunately, could not attend.
Dr F. Rose: ‘Bryophyte associations in the British Isles – some observations on community structure.’
While much work has been carried out on the Continent on bryophyte sociology, little has been done in the British Isles. A short history of foreign attempts in this direction was first given. The methods and aims of classifying and describing bryophyte communities were then discussed. The bryophyte community is a reflexion of the complex of environmental factors in its particular habitat: so, in so far as the community possesses distinctness and homogeneity, the environmental complex is a distinctive reality. Therefore any objective system of bryophyte community description and delimitation must: (1) show a reasonably constant correlation between the habitat factors and the structure of the community (a point often ignored abroad), and (2) be so designed that any other competent worker can also recognize the units and use the descriptive techniques.
To produce a satisfactory and sufficiently objective technique of description, quantitative methods must be used where possible, though the experience of the skilled field botanist in recognizing communities initially is not to be ignored.
Degree of association appears in practice to be more important than measurement of absolute cover: the latter is very difficult to carry out accurately, and very time-consuming. Units can best be determined by specific composition, but are of little objective value unless a fair proportion of the species show a high degree of constancy and indeed fidelity to the association. Simple statistical techniques for assessing degree of association and coefficient of difference were discussed, and a number of examples of well-characterized bryophyte associations with a number of species in each of high constancy, were described; examples quoted included wet-heath, Sphagnetum of acid bog, rich calcareous Schoenus-fen, and chalk grassland north slope terrace associations.
On Saturday evening, the subcommittee convened to deal with the bryophyte mapping scheme met and, later, at a conversazione held in the Botany Department, mapping cards were on sale. The following exhibits were presented: Studies of variation in Amblystegium (W. M. M. Baron); Cytological studies in the genus Dicranum (D. Briggs); Mire Bryophytes from Swedish Lappland, Mosses from British Quaternary Deposits (J. H. Dickson); British species of the Plagiothecium denticulatum-sylvaticum complex (S. W. Greene); Recent additions to the British Hepatic Flora (Dr E. W. Jones); Variation in Sphagnum imbricatum, S. strictum and S. compactum (Miss E. M. Lobley); Southbeya tophacea new to Britain (Mrs J. A. Paton); Campylopus introflexus and C. polytrichoides (Prof. P. W. Richards); Microfilm of anatomical studies of Mosses (Dr L. B. C. Trotter) (Dr Trotter has generously presented this microfilm of his work to the Society); Recent additions to the British Moss Flora (Dr E. F. Warburg); Stereoscopic colour transparencies of Tortula stanfordensis and Gongylanthus ericetorum at the Lizard, Cornwall (Dr and Mrs H. L. K. Whitehouse).
On Sunday, a fine, dry day, twenty-two members set off by coach (since private transport was not forthcoming) to White Horse Hill in Berkshire, v.c. 22. First, a stop was made in Oxford itself, where Octodiceras fontanum was seen growing on the stonework of the canal at the junction of Hythe Bridge Street and Upper Fisher Row.
The time spent at White Horse Hill gave members the opportunity to see common chalk grassland species as well as a few rarer ones, namely, Barbula acuta, Ephemerum recurvifolium, Pottia caespitosa and Weissia sterilis, all of which occurred on Dragon Hill. After lunch, the party proceeded to Cothill where the majority of members visited the gravel pits. The most noteworthy species found were Bryum intermedium, B. pendulum and Preissia quadrata. A few members botanized a nearby fen, dominated by Schoenus nigricans and Juncus subnodulosus, and saw various fen mosses, including Campylium elodes, Drepanocladus revolvens var. intermedius, Mnium pseudo-punctatum and Mnium seligeri.
Thanks are due to the Oxford Botany Department for supplying refreshments free of charge and Dr Warburg and Mr Smith are to be congratulated for a completely successful meeting.
James H. Dickson