Observational evidence indicating that the expansion of the universe is accelerating has surprised cosmologists in recent years. Cosmological models have sought to explain this acceleration by incorporating ‘dark energy’, of which the traditional cosmological constant is just one possible candidate. Several cosmological models involving an evolving equation of state of the dark energy have been proposed, as well as possible energy exchange to other components, such as dark matter. This paper summarizes the forms of the most prominent models and discusses their implications for cosmology and astrophysics. Finally, this paper examines the current and future observational constraints on the nature of dark energy.

While it remains the staple of virtually all cosmological teaching, the concept of expanding space in explaining the increasing separation of galaxies has recently come under fire as a dangerous idea whose application leads to the development of confusion and the establishment of misconceptions. In this paper we develop a notion of expanding space that is completely valid as a framework for the description of the evolution of the universe and whose application allows an intuitive understanding of the influence of universal expansion. We also demonstrate how arguments against the concept in general have failed thus far, as they imbue expanding space with physical properties not consistent with the expectations of general relativity.

The present paper deals with further investigations into the structure, the stratification, and the plant remains of peat deposits, carried on in various districts during 1907, 1908, and 1909.

The objects of the research, stated briefly, are to determine, as far as the state of preservation of the material permits, the history of the flora on peat-covered areas since their formation during the later stages of the glacial period. This really resolves itself into a research dealing with the changes in distribution undergone in post-glacial times by part of the British flora.

During 1904 and 1905 the author investigated the plant remains of the peat deposits in certain areas of the Southern Uplands and the Highlands. The present paper deals with similar work over large peat-covered areas in the E. and N. W. Highlands, Shetland Islands, and the Outer Hebrides.

Perhaps the most interesting feature found in the course of the work is the evidence of constant change in the character of the vegetation which has successively covered the peat areas of Scotland. Many areas in different parts of the country have been examined in order to ascertain if this succession can be accounted for by local changes in physical conditions, or whether it represents stages in a long cycle of secular changes in climate, and consequent plant migrations.

An investigation of the peat mosses in some districts of the Scottish Highlands was made in 1905, with a view of comparing the features found there with those already recorded from the Southern Uplands in 1904. The salient feature met with in the Southern districts was the existence in all the older mosses of an upper and lower forest-bed, with a zone of Arctic plants intercalated between. The existence of this Arctic plant bed, stretching at the same horizon through the peat in districts widely separated, indicates a lowering of temperature which must have obtained over much greater areas; for the conditions implied by the presence of an Arctic vegetation at low levels in the South of Scotland would suffice—precipitation being great enough—to produce glaciation in the Highlands.

The following paper deals with an investigation of the successive zones of plant remains contained in the deeper peat deposits covering areas in the Scottish Southern Uplands. The field work was carried on during the summer and early autumn of 1904, and the detailed examination of the peat in the laboratory during part of the winter. No attempt has been made to work out the detailed flora of the different zones, but attention has chiefly been directed to the dominant plant remains found at different horizons in the mosses. Whilst the list of plants from each zone is small, the general facies of the flora of any layer can be gauged from the abundant presence of a few characteristic plants such as Salix reticulata and Empetrum, or Sphagnum and Eriophorum. Thus, while the investigation is incomplete as regards any addition to the history of the British Flora, it will, I hope, throw some light upon the succession of vegetation over the older peat mosses since their origin.