. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . & G. S. West. O, Spondylosium rectangulare(Wolle) W. & G. S. West, a, front view; b, vertical or end view; c, side view; d, basal viewof seniicell. A and B, x 333; C—O, x 433. Sooner or later the other pole becomes similarly attached and furtheroscillatory movements are carried out. Sometimes, as Stahl showed inCl. moniUferum, the cell swings completely over through 180° and then DesmidiacesB 361 becomes attached by the other pole, the moveme
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . & G. S. West. O, Spondylosium rectangulare(Wolle) W. & G. S. West, a, front view; b, vertical or end view; c, side view; d, basal viewof seniicell. A and B, x 333; C—O, x 433. Sooner or later the other pole becomes similarly attached and furtheroscillatory movements are carried out. Sometimes, as Stahl showed inCl. moniUferum, the cell swings completely over through 180° and then DesmidiacesB 361 becomes attached by the other pole, the movement being repeated. Thisreversal of position occupies from 6 to 35 minutes according to the tem-perature, the change of position occurring more rapidly as the temperature isincreased. At 33° C. the reversal occupied from 6 to 8 minutes. In a numberof other genera, such as Gosmarium, Euastrum, Micrasterias, etc., the move-ments are mostly quite irregular and spasmodic, although sometimes of agliding character. In greatly compressed Desmids the flattened sides maybe kept towards the incident light. The movements have been chiefly ascribed. Fig. 225. A and B, Onychonema compaction W. & G. S. West. C—F, 0. laeve Nordst.; D and-B, zygospores; F, aplanospore. G, O. Iseve Nordst. var. latum W. & G. S. West. H, G. C. Wallich. a, front view; b, vertical or end view. E, x 360; all theremainder x 468. to heliotropic and geotropic responses, but there is little doubt that in mostcases the spasmodic nature of the movement is owing to the secretion of anirregular stalk of mucilage through the larger pores at the extremity of thecell (fig. 228 A), and that, moreover, a substratum is necessary for the move-ment to be carried out. If a sediment of organic detritus containing anumber of living Desmids be exposed to the light, in a few hours the Desmidswill have moved towards the incident light, having collected in clusters sur-rounded by abundant mucilage. 362 Conjugate In
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