Taxonomic studies of Betula with particular reference to Betula pendula Roth and Betula pubescens Ehrh

Atkinson, Robert Thomas (1976) Taxonomic studies of Betula with particular reference to Betula pendula Roth and Betula pubescens Ehrh. MSc(R) thesis, University of Glasgow.

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Tree birch from within the British Isles have been examined cytologically, morphologically and chromatographically. Studies have also been made of the reproductive biology of Betula. Cytology confirms that difficulties are associated with chromosome number determination in Betula because of the small size of chromosomes in the genus. It is suggested that two cytodemes have been identified having chromosome numbers 2n=28 or 2n=56. The evidence for aneuploids is not persuasive from present studies in view of the ambiguity of some chromosome preparations. No plants with a chromosome number 2n=42 have been found in the samples studied. Trees having normally accepted morphological characteristics of Betula pendula and B. pubescens together with trees apparently intermediate in terms of these characters have been found on the disturbed area of ground at Drumclog Moor near Glasgow. Various statistical methods have been used in the study of the morphology of birch. Both diploid and tetraploid trees have been found to be variable. In many causes the ranges of variation in a given character for the two groups show considerable overlap. Certain accepted criteria for distinguishing birch species have been found to be of little value in the present studies. It has been established that cross-pollination may take place between B. pendula and B. pubescens in certain areas examined. This does not ensure, however, that fertilisation and the successful production of hybrids takes place in nature. Pollen studies have been made to investigate the possibility that "giant grains" are produced. In view of the size of the sample and the fact that there is a considerable overlap in the sizes of pollen grains of B. pendula and B, pubescens, firm conclusions cannot be drawn from this area of work. The viability of seeds has been investigated by measuring seed germination. It has been found that the germination success of birch seeds is very variable. A chromatography technique has been developed which is apparently capable of distinguishing leaf extracts of B. pendula from those of B. pubescens. In a majority of cases the classification of birch on the basis of chromatography has agreed with the classification made from cytology and morphology. In a few cases a tetraploid plant has had the chromatographic pattern which characterises the diploid. It has frequently been stated in the literature that hybridisation occurs in birch, although supporting evidence is difficult to obtain. The present studies are consistent in several ways with the concept of hybridisation but it must be stressed that a relatively small number of plants have been examined. More work is required to determine the extent of variation in birch throughout its range.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: M B Wilkins
Keywords: Botany
Date of Award: 1976
Depositing User: Enlighten Team
Unique ID: glathesis:1976-72956
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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