. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . he protoplast of eachcell forms two gametes by division. Thegametes of the two cells fuse in pairs formingtwo zygotes, each of which develops into anauxospore. This type has been observed inAmphora ovalis,Epithemia Argus,Rliopalodiagibba, Navicula limosa (fig. 78 J.), and a fewothers. The cytology of the conjugation hasbeen followed out by Klebahn (90) in thecase of Rliopalodia gibba. The protoplastsof the two cells become closely approximate
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . he protoplast of eachcell forms two gametes by division. Thegametes of the two cells fuse in pairs formingtwo zygotes, each of which develops into anauxospore. This type has been observed inAmphora ovalis,Epithemia Argus,Rliopalodiagibba, Navicula limosa (fig. 78 J.), and a fewothers. The cytology of the conjugation hasbeen followed out by Klebahn (90) in thecase of Rliopalodia gibba. The protoplastsof the two cells become closely approximated,and the nucleus of each protoplast dividesfirst into two and then into four. Two ofthese nuclei soon become reduced in sizewhile the other two are conspicuous by theirlarger size. Each protoplast now dividesinto two portions, each of which containstwo nuclei, one large one and one small halves of the approximated protoplastsnow coalesce, the larger nuclei fusing whilethe smaller nuclei gradually disorganize(fig. 79). The important feature thus broughtto light by Klebahn is the division of thenucleus of the original protoplasts into four,. Fig. 78. A, Navicula limosa Kiitz.( x 450). B, Achnantkes flcxella(Kiitz.) Breb. ( x 450). C, NaviculaAmphisbsena Bory ( x 450). D, Kiitz. (x 350). C and Dillustrate the first method of auxo-spore-formation, B the third method,and A the fifth method. A uxospore formation 109 and the significance of this tetrad-division, which precedes conjugation, maylie in the reduction of chromosomes. There yet remains much work to be done on the cytology of auxospore-formation, as most of our present knowledge is based upon a few isolated cases.
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