The introduction contains an appreciation of the work of James Ritchie (1882–1958) on hydroids. His collections in the Royal Scottish Museum consisting of 266 species have been re-examined and listed with up-to-date synonymy, this also serving as a catalogue of all the identified hydroid material in this Museum.

Among the important collections are those made by W. S. Bruce in the Scotia and E. H. Shackleton's Antarctic Expeditions; there is also much valuable secondary material, especially in the form of micro-preparations, from collections reported on by Ritchie, notably those of the Australian Thetis Expedition, the Scottish Loch collections of Sir John Murray, the Indian Museum and collections by Cyril Crossland, James Simpson and Rudmose Brown and others.

Ritchie described many new species and varieties and all the type material has been noted, lectotypes being designated where necessary.

Hydroids from the Goldseeker collections of the Fishery Board for Scotland were not reported on by Ritchie although he identified a considerable number of samples from Scottish waters—these have been included in this survey. These new records are of considerable value for compiling distribution lists. Apart from Ritchie's own work little has been done on hydroids from waters around the north of Scotland since the days of Hincks, Allman and Norman. The bibliography contains a full list of James Ritchie's hydroid papers.

The species composition and succession of the algal plankton are described. Population density changes, as indicated by chlorophyll a, cell volume and numbers are discussed in relation to physical, chemical and biological factors in the environment.

The quality and the amounts of the plankton vary considerably from year to year. However, for most of the period reviewed it has been dominated by dense developments of nanno and other small algae belonging to the diatom and blue-green groups.

Factors of particular importance affecting the high observed biomass and production include the water depth, adequate mixing and a rich supply of nutrients from the inflows and the sediments. Competition from other green plants appears to be low. Utilisation of living algal cells in the plankton by crustacean and protozoan grazing and fungal parasitism is rarely important.

The composition of the phytoplankton is discussed in relation to the eutrophic nature of the loch.

Because of both the energy costs and the slowness of the reactions of the nitrogenase complex compared with those involving some form of combined nitrogen (oxidised or reduced), we argue that the evolution of nitrogen-fixing organisms required an environment which was very limited in combined nitrogen. This is thought to have occurred after phototrophy evolved, but before water was used as a hydrogen donor (and therefore oxygen was present in the atmosphere). After oxygenic photosynthesis evolved, the need for a high level of biological nitrogen-fixation remained, since abiotic inputs were insufficient to keep pace with the rapidly evolving biomass (flora and fauna). Symbiotic fixation probably first evolved in the form of casual associations between cyanobacteria and most other groups of plants. By inhabiting the sporophytic generation of evolving land plants (cycads in particular), protection against nitrogenase-inactivating oxygen and a more desiccating environment was achieved simultaneously.

We envisage nodulated plants arising by the transfer of nif genes into tumour-forming bacteria. In the case of legumes, these would be ancestors of extant agrobacteria, which gain entry into their hosts via wounds. Co-evolution of symbionts from nitrogen-fixing tumours has taken several routes, leading to extant nodules differing in mode of infection, structure and physiology. Evolution towards optimisation of oxygen usage is continuing.

Nitrogen-fixing symbiosis in animal systems is only advantageous in specialised ecological niches in which wood is the sole dietary intake. In the case of shipworms, the symbiosis has many of the advanced features associated with nitrogen fixing root nodules.

Various lines of evidence suggest that the controlled increase in the production of oxygen radicals is an important factor involved in phytohormone metabolism, selective changes in membrane permeability, degradation of photosynthetic pigments and unsaturated membrane lipids, oxidative modification and subsequent proteolytic degradation, and other events occurring in ageing and senescing leaves. Increased lipid peroxidation, appearance of chlorophyll allomerised products, as well as fluorescent ‘lipofuscin-like’ pigments have been documented in different systems of leaf senescence. On the other hand, the accumulation of peroxidised products may result from the alteration to native structural organisation and energy dissipation reactions of the photosynthetic apparatus. Although there are contradictory and incomplete data on the activity of the systems involved in the metabolism of oxygen radicals, it seems that senescing leaves retain, at least in part, their defence potential against both activated oxygen species and toxic lipid peroxidation products. This provides the plant with the ability to successfully dismantle its photosynthetic apparatus during senescence in a relatively safe manner.

All plants are able to survive anoxic periods, but the degree of tolerance shows large variation. The main injuries related to anoxia are eventually due to changes in energy metabolism. Low energy charge values indicate a cessation of many ATP consuming processes. Sugar starvation, lactic acid fermentation and proton release from leaky vacuoles are responsible for cell death. Long-term anoxia tolerance is dependent on storage products in the vicinity of sinks, on an adequate control of glycolysis, synthesis of essential proteins, and stability of membranes and organelles. However, no fundamental differences between the metabolic pathways of tolerant and non-tolerant tissues are known. It is rather a question of minor changes and the regulation of anaerobic metabolism.

Re-exposure of anoxic tissues to air may even be more detrimental than anoxia itself. These injuries are mainly due to enhanced radical generation. Lipid peroxidation processes lead to membrane damage, disintegration, and leakage of solutes. Under natural conditions plants are equipped with radical-detoxifying systems (SOD, peroxidases and antioxidants). Natural detoxifying systems can be reduced in non-adapted plants under anoxia and they become more sensitive to post-anoxic damage. In addition, the rapid conversion of ethanol to extremely toxic acetaldehyde seems to be a cause of tissue injury and death.

A study has been made of the supply and utilisation of nitrogen and phosphorus in Loch Leven, a shallow eutrophic lake receiving discharges from sewage treatment plants, industry and agricultural sources. Calculations of the nutrient budgets over a period of several years indicate that nitrogen enters primarily as nitrate derived from agricultural fertilisers, in quantities more than sufficient to sustain the dense algal blooms which occur. Much of the nitrate appears to be removed by benthic algae, or other processes associated with the sediments, and a high proportion of the incoming nitrogen is retained in the lake.

Phosphorus enters the lake mainly from industry, with some contribution from sewage and agriculture, and a high proportion is discharged at the outflow. The algal blooms require more phosphate than is present in solution initially, and utilise it at rates greater than that of the inflowing sources, and it is deduced that the additional phosphate is derived from the sediments. A mechanism for such a release, occurring in the absence of stratification, is postulated, and the processes involved in the return of phosphorus to the sediments are discussed.

Muller's classical discovery in 1927 of the mutagenic action of X-rays has provided an extremely useful tool for studying the nature of gene mutation and chromosome breakage. It has always been realized that if, in addition, chemical substances were found capable of producing mutations and/or chromosome breaks a further important step forward in the analysis of the mutation process would follow. The search for such mutagenic substances has therefore been going on in various laboratories for some ten years, until recently, however, without definitely positive results. Only during the last few years has it been shown that certain chemical substances, such as mustard gas (ββ′-dichlordiethylsulphide, (ClCH2 · CH2)2S), may be as effective as X-rays in producing mutations and chromosome breaks (Auerbach, 1943; Auerbach and Robson, 1944; Auerbach, 1945; Auerbach and Robson, 1946). Indeed, the similarities between the results of these two types of treatment are impressive. In the course of more than four years during which work of this kind has been carried out by the author, only few differences between the genetical results of chemical treatment and of irradiation have come to light. Particular interest attaches to these dissimilarities, because they, rather than the many similarities, may throw some new light on the process of mutation and through this on the nature of the gene. One of the few striking dissimilarities is the high frequency of certain types of mosaics which can be produced by chemical treatment. It is the object of the present paper to summarize the data on chemically induced mosaicism, contrast them with similar data from X-ray experiments, and discuss the similarities and differences from the point of view of the mechanism of induced mutation.

The Labiatae of SW Asia arc analysed. There is a major development of the family in this area with c. 1100 species, much morphological diversity, many illuminating distribution patterns and very high endemism levels; species endemism averages over 70% in the medium-sized and large genera. Areas of high concentrations of endemic taxa are indicated. The very significant differences between the Labiate floras of Turkey, Iran and Afghanistan throw doubt on designating all the steppic part of the area as Irano-Turanian; there is a strong Mediterranean floristic connection throughout much of Turkey and little evidence of Irano-Turanian influence. There are numerous taxonomically very isolated genera and species; some of these genera have very restricted distributions, a few are almost cosmopolitan.

The occurrence of ectomycorrhizal fungi in West African rain forest systems is demonstrated and linked to the presence of a range of caesalpinoid legumes and to members of the genus Uapaca. The vast array of boletes, members of the Russulaceae and Amanitaceae, and chanterelles is described. The virtual absence of ectomycorrhizal Cortinariaceae is emphasised. After an overview three separate yet interlinked studies are described: a survey of ectomycorrhizal fungi throughout the region (Thoen): ectomycorrhizal fungi of a single rain forest community (Watling) and the significance and relationships of the genus Russula in the Guinea–Congo Region (Buyck). Some comparisons are made with other rain forest areas of the world.

A method is presented by which the sampling variance of all heritability estimates derived from ratios involving variance components may be found.

Astragalus, excluding Astracantha (formerly Astragalus subgenus Tragacantha), has a world total of c. 2500 species, of which c. 500 are in the New World; it is one of the largest genera of flowering plants. The estimated number of species in the Flora Iranica area is c. 900–1000. Because of the huge size of the genus, no one person is familiar with all its groups; although 150 sections have been described, many are poorly delimited, often not typified and many untenable. In the Old World the genus is almost entirely restricted to the northern hemisphere. Sections with primitive characters mostly contain mesophytic species widespread in mountains and relatively humid regions; in the more advanced sections the species are adapted to dry or arid conditions.

Only a few sections are strictly endemic to the Flora Iranica area (e.g. sects. Microphysa, Acanthophace, Leucocercis). In 2 of the better known large sections (Astragalus and Caprini) there are 2 main centres of diversity: the Armenian knot and the Zagros mountains; Afghanistan and the adjacent Pamir-Alai region. Their patterns of distribution and migration are probably repeated in several other sections in the genus.

Studies in the variation of the Anthracosiidæ (= Carbonicolidæ) in the South Wales Coalfield by Davies and Trueman (1927) and in the Scottish Coalfields by Leitch (1936, 1940, 1941) have suggested that environmental influence on shell form is confined to changes in thickness of shell and in obesity. Davies and Trueman quoted H. R. Wakefield, who remarked that to-day among the Unionidæ these characters appear to vary according to the station of the shells in a single lake. Leitch referred to the work of Ortmann (1920) on the relation between obesity and distribution of river mussels in a large drainage basin in the U.S.A. The writer, in the course of very detailed work on the most highly variable faunas of the Anthracosiidæ known in the British Coal Measures, found evidence suggesting that certain other changes in shell shape and dimensions may also accompany environmental changes, as far as past environments may be reflected in the lithology of the rocks containing the shells.

The inter-relationships of ten strains of blight (Phytophthora infestans) and four major genes, R1, R2, R3 and R4, controlling resistance to the disease in potato foliage are examined. The complete differential host series for this material numbers sixteen, and is capable of differentiating sixteen strains of the pathogen. The reactions exhibited by the series form a concise statement of the various relationships and provide a genetical basis for the systematic classification of strains. This classification affords a means of calculating the segregation-ratios to be expected from the mating of any pair of genotypes when infected with any strain or group of strains of the parasite.

Each strain, being adapted to a particular Solanum genotype, is more prolific on it than on any other. This genotype is regarded as the natural host of the strain in question. Specialisation, of the parasite appears to progress in stages in certain directions determined by the genetic constitution of the various hosts.

A review of the literature on forest soil change in North America, Central Europe. Sweden, U.K., and Australia reveals that changes are occurring in both polluted and unpolluted sites at a greater rate than previously suspected. Acid deposition has played a major role in recent acidification in some areas of Europe and, to a more limited extent, in Sweden and eastern North America. However, rapid rates of soil acidification are occurring in western North America and Australia due to internal processes such as tree uptake and nitrification associated with excessive nitrogen fixation. The presence of extremely acid soils is not necessarily an indicator of significant acidic deposition, as evidenced by their presence in unpolluted, even pristine forests of the north-western U.S.A. and Alaska. Numerous studies in Sweden, Australia, and North America show the important effects of tree uptake and harvesting upon soil acidification in managed forests. Furthermore, arguments can be presented that harvesting takes a greater toll upon the pools of potentially limiting cations than leaching.

The rate at which soils are changing in some instances calls for a re-evaluation of the budget analyses used to predict soil change. Specifically, inter-horizon changes due to uptake and recycling by vegetation, the interactions of such changes with naturally- and anthropogenically-produced acids, and the effects of aluminium uptake and recycling need further evaluation and study.

The extent of occurrence, the form and the function of mycorrhizal infection are shown to change with successional development across coastal sand dune systems. The interrelationships between these changes and the prevailing physico-chemical conditions are explored and clear patterns are recognised in terms of both type and function of the infection. The periodically disturbed and nutritionally enriched high tide line is colonised by non-mycorrhizal ruderal species. There follows a sequence of plant communities, each characterised by the presence of a dominant mycorrhizal type and a distinctive nutritional limitation. In the foredunes, pioneer grasses are normally infected with vesicular-arbuscular (VA) mycorrhizal fungi. Plants such as Ammophila, Leymus and Uniola, all of which have extensive root systems, appear, when fully grown, to be only facultatively mycorrhizal. However, experimental evidence suggests that infection is important for the early growth of such plants and it is suggested that in these, as in many other dune species, mycorrhizas may be essential at critical stages in the life cycle, most notably during the phase of seedling establishment. Here, phosphorus (P) is the most important growth-limiting nutrient. The extensive mycelial network of VA hyphae not only facilitates capture of this element but also provides the aggregation of sand grains necessary for dune stabilisation. In semi-fixed dune pastures, as sand inputs are reduced, productivities are low and species diversity increased. Phosphate limitation persists and the majority of the characteristic species show VA infection. Experimental studies using microcosms of dune sand containing an assemblage of species typical of such communities suggest that the maintenance of the species richness is dependent upon mycorrhizal fungi which produce a large absorptive mycelial network into which the roots of germinating seedlings become incorporated as they are infected. Accumulation of organic matter in dune-slacks leads to reduction of pH. Nitrification is inhibited, ammonium becomes the major mineral nitrogen (N) source and N replaces P as the key growth-limiting element. Here plants with ecto-mycorrhizal infection predominate. Salix repens produces a shrub layer enriched with litter in which a guild of species interconnected by a common mycorrhizal mycelium occurs. The functional basis of this guild structure is explored, the ability of some of its mycorrhizal fungi to mobilise nutrients from organic macro-molecules being seen as a vital attribute. Where organic matter accumulation and base depletion are most strongly developed in the oldest parts of the succession, plants with ericoid mycorrhizas become important. The ability of their mycorrhizal fungi to liberate N and P from acidic organic complexes, as well as to assimilate or exclude, and hence detoxify, organic acids and metal ions facilitates vigorous growth of ericaceous species in soil conditions which are inimical to plants important earlier in the succession. Since the attributes of each mycorrhizal type are relevant to a specific suite of edaphic properties the formation of appropriate symbiotic associations is likely to be a prerequisite for successional change. It is concluded that mutualism contributes significantly to fitness in the sand dune ecosystems, the further understanding of which will be dependent upon more effective collaboration between the microbiological and ecological disciplines.

I want to give a brief resumé of the reasons why the taxonomic study of Salix is so notoriously difficult. As long ago as 1737, Linné in Flora Lapponica wrote: “Hunclocum sibi postulat Salicum familia, qui si ulla in Botanicis obscura, haec sane maxima”. The phrase “crux et scandalum botanicorum” has been quoted time and again.

(1) All willows are dioecious, developing male and female flowers in different individuals.

(2) Flowers in many species are precocious, the flowers appearing before the leaves.

(3) There is a tendency for the current year's terminal and past year's lateral branches to differ in indumentum, leaf shape and leaf sequence.

The electrolytic reduction of oxygen which occurs at a wetted ‘unattackable’ cathodic electrode of platinum or gold when polarised in conjunction with a Ag/AgCl anode, forms the basis of most polarographic oxygen measurements in plant biological work.

Various types of polarographic electrode and their uses are reviewed. These include cylindrical sleeving electrodes for quantifying localised oxygen fluxes from intact roots, ‘bare’, membrane-coated, and Clark-type microelectrodes suitable for measuring concentrations and profiles both inside roots and in the rhizosphere, and macro-Clark electrodes most frequently used in respiratory studies.

Some details concerning equipment and electrode construction are given and some pitfalls in electrode application are discussed.

At a height of 4400 metres in the Nepal Himalaya, a vitreous and vesicular rock was discovered by J. S. Scott in 1949. It is located along a line of intense brecciation in a region of high-grade granitic gneisses.

This paper is based on a laboratory examination of a specimen of this rock and a few other specimens from the same locality. As some of these specimens have no exact counterpart hitherto described, a new but self-explanatory nomenclature has been employed in their description. The new rock-types—breccia with a cryptomylonite matrix, cryptomylonite and hyalomylonite—seem to represent, in this order, progressive stages in the degree of vitrifaction.

Biotite, alkali feldspars and quartz participated in the vitrifaction, which was due to high temperatures and heat developed by friction between these minerals in a triturated rock medium of low thermal conductivity.

An important function is attributed to the biotite which, in the more vitreous parts of the rocks, tends to disappear entirely. It is suggested that selective melting of this biotite has yielded to the liquid ferrous iron, and fluxing by this component is believed to be a critical factor although water must also be considered. Chemical analysis revealed no significant quantity of water in the glass-rich rock, but the development of vesicles and bubbles implies that there was more water in solution prior to its ebullition as a vapour phase.

There appears to have been a remarkable variation in temperatures within extremely short distances, and there is some evidence that the specific melting points of the alkali feldspars may, in a few exceptional instances, have been attained.

The production of mutations by the action of chemical substances on germ cells has often been reported. However, the variability of the spontaneous mutation rate and its dependence not only on environmental conditions and physiological factors, but also on the genotype, make it extremely difficult to assess the value of tests in which only small increases over the spontaneous mutation rate have been found. For this reason, Muller was still able to conclude in 1941 that there was no definite proof that chemical substances could exert an effect on the mutation rate. Since then, Thomas and Chevais (1943) have reported results with sulphonamides which, if they can be confirmed, would indicate a real, though slight, action of these substances on the chromosomes, at least as far as gene mutations are concerned. Stubbe (1940), working on plant material, observed a significant increase in mutation rate with phenol and potassium thiocyanate. It is of interest that Auerbach and Robson (1943) independently observed a similar effect with allyl isothiocyanate in experiments on Drosophila. Even these definite effects are, however, very slight.

During the last four years we have been testing a number of chemical substances. Among these a certain group has been found which increases the rate of occurrence of mutations and chromosome rearrangements to a similar extent as that brought about by X-rays and similar physical agencies. The best known representative of this group is mustard gas, and the present report deals only with the effects produced by this substance. Results obtained with other effective substances will be published later.

The annual production of trout in Loch Leven lies between 2·2 and 3·9 g(wet).m−2, and of perch between 5·1 and 67·4 g(wet).m−2. Between June and September adult trout consumed 3·7 times their own wet body weight of food, and adult perch 6·58 times, the daily intake decreasing from the beginning to the end of the period. The principal dietary components of the two species were the same, Asellus and perch fry being quantitatively the most important. Comparisons are made between field estimates of food consumption, laboratory estimates of food requirement, and field estimates of food production.