The ecotypic differentiation of populations: Altitudinal distribution of variation in Festuca

The investigation of the chromosome numbers of the fescue populations on Ben Cruachon shows that there are several distinct chromosome races. The setaceous-leaved sexual fescues are almost entirely diploid but a tetraploid also occurs; the broad-leaved sexual fescues include hexaploid and octoploid races as well as some heptaploids: the viviparous rescues are without exception tetraploid. 2. The viviparous fescues may be found throughout the area and occur all along each of the three gradients. In the sotaceous-leaved sexual fescue the tetraploid occurs at sea-level but the diploid race extends as high as 2,600 feet on Ban Oruaohon. The hexaploid race of broad-leaved sexual feseue has a range coincident with that of the sexual diploid although its occurrence on the hill is rather sporadic and the plants are rather difficult to identify. The octopiold and heptaploid races of the broad-leaved sexual fescues occur only at sea-level. 3. Chromosome counts of setaceous4eaved sexual fescues from various parts of Scotland, the Scottish islands, England and Wales indicate that the two chromosome races have a definite pattern of geographical distribution. The diploids occur in the North and islands whilst tetraploids are found in the South of Scotland, England and Wales but further investigations are necessary before any definite conclusions can be drawn. 4. The setaceous-leaved sexual fescues have been found to be capable of free interbreeding but are sexually distinct from the broad-leaved sexual rescues. 5. The hereditary variation which is present in each population makes it difficult to fit the plants into taxonomic groups but for reference purposes the setaceous-leaved sexual rescues are called Festuca ovine, the broad-leaved sexual rescues, Festueca. supra, and the viviparoue feeoues, yestuca yivipore. 6. A key for the identification of British viviperous fescues adapted by Wilmott from that proposed by Turesson is given in full and its application to the viviparous rescues from Ben Cruachan discussed. 7. The distribution of hereditary variation in F. ovina, F. rubre. and F. va on the three gradlente is discussed in the light of the statistical results obtained from the measurement data and an attempt is made to deduce reasonable, explanations through correlation with environmental conditions. 8. The problem of the origin of hereditary variation in the viviparous rescues is discussed: mention is made of the occurrence of partial and complete sexual flowers on hunger inflorescences late in the season and also of the production of completely sexual plants from the bulbils of a viviparous plant. 9. The taxonomic units of species, subspecies and variety are discussed with special reference to the possibility and advisability of equating them with the units of experimental taxonomy. 10. The numerous difficulties involved in taking into account the hereditary variation in populations can only be adequately resolved by applying the concept of the character gradient with reference to the related environment influence 11. The areal ecotype is a useful but limited concept since the information which it supplies is little more than that the population in question is tolerant of the ecological conditions. The acoclinel, however, takes into consideration the trends of hereditary variation which occur along an environmental gradient, end ecpclInpl"esatue4mav be defined for reference purpose. It is understandable that where a number of creel populations are investigated they way be found to occur on an environments gradient end they may in that ease be called ecoclineal subspecies such a classification permits of further definition within each ecoclinal subspecies of internal trends of variation. 12. The distribution of the hereditary variation within the fescue populations (F. ovina and V. vivioare) of Den Oruachan in respect of habit of growth may he defined as following a climatic gradient. In this case, three ecoclinal ecotypes have been named for reference purposes, erecta, ascrindent, end decumbent'. The climatic ecocline in respect of habit of growth is quite plain in spite of some irregularity at the lower levels, an irregularity which in part, at any rate, is probably due to the small else end comparative isolation of the populations. Climatic ecoclines in respect of several other attributes may also be traced. 103. 13. The chromosome races within F. rubra which occur at sea-level may be found to have distinct habitat preferences but no definite statement can be made until further research which is now being carried out, has been completed. 14. A review of the situation makes it clear that the units of orthodox taxonomy and those of experimental taxonomy must remain distinct. The classification of orthodox taxonomy has proved its usefulness and will continue to do so but the knowledge gained through the genecological approach will supplement it in a most valuable manner, 15. The study of trends of variation is not only of very great academic interest but it can also provide important data which are vital for the work of the plant breeder and for the economic success of agricultural crops