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Natural history and parasitism of Geocaulon lividum (santalaceae) Warrington, Patrick Douglas

Abstract

The natural history, structure and parasitism of Geocaulon lividum (Richardson) Fernald of the Santalaceae are described. Both the present study and that of Piehl (1963) maintain the generic segregation of Geocaulon and Comandra. All available data on the distribution of Geocaulon are presented in a series of Maps, in the accompanying text and in an Appendix. The data are drawn from the literature, from herbarium material and from field work. The only vegetation zones of Canada in which Geocaulon is not commonly found are the prairie grasslands, the arctic and alpine tundra and the west coast Douglas Fir and Hemlock forests. The ecological conditions under which Geocaulon is usually found are noted. A list of known hosts is given; many of them represented by voucher specimens in the herbarium of the University of Lethbridge (LEA). Anatomical and morphological data on the various portions of the Geocaulon plant are presented under a series of topics: rhizome, short-shoot, aerial shoot, leaf, inflorescence, flower, fruit, and root. These descriptions are accompanied by illustrative material in the form of figures, plates and photographs. Criteria for estimating the age of rhizomes and short-shoots are given along with a series of representative short-shoots with age determinations. Illustrations also indicate some of the diversity in the appearance of the inflorescence units. The haustorium is described in some detail. It is treated under several topics: general characteristics, development and structure. The structure is treated first under outer cortical region and second the, inner vascular core. The core is further divided into the mother root, transitional and haustorial zones. The distribution pattern of vessel elements within the core region is graphed. A brief discussion is included of as yet unresolved problems associated with the structure and function of the haustorium of most Santalaceous root parasites. Some previously unreported types of thickenings on parenchyma walls were found in rhizomes and short-shoots of Geocaulon. These were found mostly on cortical cell walls but were also found on the walls of other tissues. A microchemical investigation was undertaken to characterize these wall thickenings. They were found to be holocellulosic but were not assigned to either the hemicellulose or cellulose fractions. They were not composed of alpha-cellulose, the major structural material of plant cells.

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