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Desmids of some lakes in southwestern British Columbia with observations on Triploceras in culture Gerrath, Joseph Frederick

Abstract

Algal collections from eight lakes in southwestern British Columbia have been examined. The desmid flora consists of 205 species and 44 varieties in 26 genera. Two genera, Spino-closterium and Spinocosmarium, and several species of other genera, are reported for the first time from British Columbia. Seasonal changes in the abundance and kinds of desmids occurring in collections are noted. Cultural studies on the variability of Triploceras gracile and T. verticillaturn were undertaken to determine the validity of subspecific characters used in the genus. These studies showed that the apical radiation of the semicell (the number of lobes at the end of the semicell) can vary from biradiate (2-lobed) to quadriradiate (4-lobed) within a single clone. Thus in the genus this character must be discarded as a taxonomic criterion. The morphology of the protuberances of the semicells was constant in both species, and is a useful subspecific character. A number of abnormal forms occurred in cultures but were not observed in field collections. The nuclear cytology of Triploceras was investigated. T. verticillaturn has the largest chromosomes yet reported for the Desmidiaceae, almost 20 u in length measured at late prophase in colchicine treated cells. The chromosome number for this species is n = 15-20. The chromosomes of T. gracile are smaller, but no chromosome counts were obtained for this species.

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