The Gulf of St. Lawrence has a moss flora of 522 species. Of these, 217 (42%) are disjunct to this region from western North America, eastern Asia, or Europe. The Gulf of St. Lawrence and eastern North American distributions of the disjuncts were analysed and their possible migrational and dispersal histories during and after the Last Glaciation (Wisconsin) were examined. Based on eastern North American distribution patterns, the disjuncts fell into 22 sub-elements supporting five migrational/dispersal histories or combinations of these: (1) migration from the south, (2) migration from the north, (3) migration from the west, (4) survival in refugia, and (5) introduction by man.

  The largest groups of disjuncts have eastern North American distributions supporting either postglacial migration from the south, or survival of mosses in Wisconsin ice-free areas of the Gulf of St. Lawrence. About 23% of the disjuncts have complex distributions which suggests they support two possible histories. These may have migrated to the Gulf from the west and/or north, or from the west and/or survived glaciation in Gulf ice-free areas. The eastern North American distributions of some species in these groups suggest that survival in ice-free areas best explains their presence in the Gulf of St. Lawrence. Human introductions to the Gulf and migration from the north are relatively unimportant migrational/dispersal histories for disjuncts in the region. No mosses supported the hypothesis of long distance dispersal to the Gulf of St. Lawrence.

  Within the Gulf of St. Lawrence, species having migrated from the south generally show widespread distributions or occur primarily in the southern portions of the study area. Mosses introduced to the Gulf by man occur in eastern Newfoundland and in central Nova Scotia. The remaining species groups show generally similar patterns; they are restricted to the northern half of the study area, or show disjunctions between western Newfoundland, Gaspé and, occasionally, Cape Breton.

  Important habitats for disjunct mosses are late snowbeds and limestone barrens. The disjunct mosses in late snowbeds are primarily montane species, whereas the disjunct mosses in the limestone barren habitat are predominantly of arctic affinity. The disjunct mosses in the snowbed habitat provide some of the strongest evidence for survival of mosses in Gulf ice-free areas.

  The importance of disjunctions to the phytogeography of the Gulf of St. Lawrence varies with geographical scale. Continental disjunctions are best explained as resulting from climatic and geological changes occurring since the Tertiary whereas disjunctions at the eastern North American scale provide the best evidence for solving problems relating to Wisconsin dispersal and migrational histories in the Gulf. Moss disjunctions within the Gulf are explained adequately by climatic and ecological factors operating during the Holocene.

  Thirteen species of Sphagnum from Brazil and Ecuador are described as new to science.

  The section Platyloma Broth. in Engl. & Prantl of Sciaromium (Mitt.) Mitt. included only Sciaromium lescurii (Sull. in Gray) Broth. in Engl. & Prantl, a species endemic to eastern North America. The species is fully described and illustrated and a detailed map of its distribution is provided. The separate genus, Platylomella Andrews, is restored in order to accommodate it. Platylomella is distinct from all rheophytic taxa with limbate leaves on the basis of bistratose leaf margins and the presence of filiform paraphyllia. Sciaromium laxirete A. Abr. & I. Abr., a fossil from the Pliocene deposits of Bashkiria in the Soviet Union, is transferred to Platylomella and placed, with some reservation, in synonymy with P. lescurii. The relationships of Platylomella are discussed and the genus is transferred to the Hypnobartlettiaceae.

  A 2-year field perturbation experiment to investigate the effects and interaction of simulated acidic rain (pH 5.0, 4.0, 3.0) and lead (0, 50, and 1000 ppb Pb) on the boreal bryophyte Pleurozium schreberi (Brid.) Mitt. in a Pinus banksiana Lamb. forest was designed. No effect of lead or interaction of lead with acidity was found at the end of the experiment. Significant effects (p < 0.01, Duncan's New Multiple Range Test) were observed at pH 3.0 during the second year. As compared to the control, the biomass (kg/ha) of the green P. schreberi layer was reduced by 49.9%; Ca was reduced by 64% (ppm) or 80% (kg/ha), Mg by 40% (ppm) or 69% (kg/ha). Changes in heavy metal content are contrasting: Pb content increased significantly with increasing Pb levels in the simulated acidic rain; Zn and Cu levels increased, but Mn levels decreased at pH 3.0 as compared to the controls. Decreased nutrient retention by the bryophyte layer as a result of increased acid precipitation might affect tree productivity and post-fire successional stages.

  The following lichens have been analysed for steroids and nortriterpenoids by GC/MS: Evernia mesomorpha, Lecanora stenotropa, Leptogium saturninum, Nephroma helveticum, Parmelia omphalodes, Ramalina terebrata, Rhizoplaca chrysoleuca, Umbilicaria decussata, and Usnea antarctica. Fourteen steroids and three nortriterpenoids have been found.

  A long series of aliphatic compounds extracted from the lichen tissues of Cetraria delisei, Lobaria pulmonaria, Stereocaulon tomentosum and Usnea hirta, and released by saponification of the residues, were deduced using GC, combined GC/MS and HrMS. Main components of the isolated fatty acids and alcohols showed chain length of C18 and C20 respectively. A mixture of C28 and C29 sterols was isolated from the lichens and characterised in the same way by GC and MS. Lichesterol was found as the main sterol compound in the extracts of Cetraria delisei and Usnea hirta. Of interest is the presence of squalene and homologues in the extracts and of two sesquiterpenes in Cetraria delisei.

  The taxon Platysma thomsonii Stirton is transferred to the new genus Parmelaria Awas., and a new species Parmelaria subthomsonii Awas. is described.

  The results of an ultrastructural study on the development of transfer cells at the sporophyte-gametophyte junction of Physcomitrium cyathicarpum Mitt. are reported and discussed. Salient ultrastructural features characterize the three developmental stages. Ultrastructural attributes of the peripheral foot cells suggest that structurally reduced sporophyte of P. cyathicarpum, while exhibiting a simplified structure of the foot, has adapted itself for the maximum area of contact for the absorption of water and nutrients from the vaginula cells. During the early states of development, numerous mitochondria, ER and golgi are seen associated near the wall labyrinth. A large population of elongated plastids with a well developed grana-fretwork system and ample quantities of starch are observed in the first and second developmental stages of the haustorial foot. It is only in the third developmental stage that the plastids start degenerating. Notwithstanding the constraints of light and minimal amounts of CO₂, making the location of the green foot non-condusive to photosynthesis, starch is seen accoumulated in the plastids. This suggests the possibility of a different type of photosynthesis operative under such limiting conditions.

  Investigation of branching patterns, morphology, karyotype, isozymes and shoot growth confirmed specific differences between Limbella tricostata (Sull.) C. M. and L. fryei (Williams) Ochyra. Significant differences were observed in branch bud frequency, leaf insertion angle, leaf areolation, chromosome length, electrophoretic mobility of superoxide dismutase, and shoot regeneration. Chromosome numbers of both taxa are n = 11. A key and descriptions segregate the taxa.

  (1) A new genus Pseudotaxiphyllum Iwats. was segregated from Isopterygium. The new genus is easily distinguished from Isopterygium by having gemmiform propagules, well differentiated annuli, mostly dioicous inflorescence, and by lacking pseudoparaphyllia on stems and branches. Seven species were transferred to the new genus from Isopterygium. Six species were reduced to the synonymy. (2) A new combination, Isopterygiopsis pulchella was made. The species has papillose rhizoids from leaf axils, differentiated annuli, and filamentous propagules, but no pseudoparaphyllia on branches and stems. These characters are similar to Isopterygiopsis muelleriana.

  Chromosome numbers of 28 taxa of Plagiothecium, Herzogiella, Isopterygiopsis, Isopterygium, Pseudotaxiphyllum and Taxiphyllum were investigated. Together with previous reports, chromosome numbers of 36 taxa of this taxonomically difficult group of mosses have now been reported. Cytotaxonomically the species of this group are very similar, and they have a similar karyotype formula.