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Title: Variation in structure of the secondary xylem in individual dicotyledonous trees
Author: Rao, Bendapudy Sundarasiva
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1959
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Variation in structure of the secondary xylem was studied in the hole, branches and roots of Quercus robur L., Fagus sylvatica L., Acer pseudoplatanus L., and Robinia pseudoacacia L. Attention was paid especially to variation in the length of the vertical elements, diameters of the vessels and to ray height and volume. Vessel-elements and libriform fibres increased in length from the pith outwards at any one level in the bole, branch and root, at first rapidly and then rather slowly. In a specific growth ring these elements increased in length upwards in the bole up to a certain height and later decreased. It is suggested that the fusiform initials of the vascular cambium become larger during the first few years when growth of the tree is most vigorous, thus accounting for increase in length of the derived elements from pith outwards at any one height; further, that successively larger fusiform initials are laid down nearer the apex during the period of greatest vigour so that at this time the longitudinal elements in a ring are longest nearer the apex. After this periodof maximum vigour is past, new fusiform initials are smaller and hence the longitudinal elements of the xylem are smaller above a certain height. Vessel-elements and libriform fibres within one growth ring are longer in the late-formed wood than in the early-formed wood irrespective of whether the vascular cambium is stratified or not. The variation in the length of the vessel-elements is correlated with the diameter of the vessel, those of the spring wood shortening as a result of the considerable swelling during differentiation. On the other hand, the libriform fibres elongate during differentiation. Variation in vessel diameters, ray height and ray volume show much the same trend as that of the vessel-elements. Apart from certain minor details, wood of different ages and that from different parts of the tree, shows no great histological difference.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Botany