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Various experiments have been conducted on the ecology and biological activity of Rosalina columbiensis (Cushman). Light produces no apparent response, except as a secondary response to the main food source utilized, diatoms. Substrate composed of sand appears less advantageous than a fine-grained substrate because of the obstacles to movement, mechanical agitation, and relatively low standing crop. Higher temperatures resulted in a faster growth rate and slightly larger chambers. The relationship of R. columbiensis to Tretomphalus was proved by the appearance of the agamontic generation possessing the final, large float chamber. These individuals occur within the life cycle of R. columbiensis and constitute up to 20 per cent of the total culture population. The "normal" . columbiensis reproduces agamontically until conditions are available to produce the gamontic generation.
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