. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . of conjugation. Of these theMesocarpese is the lowest group and theSpirogyreas the most advanced. Sub-family MESOCARPETE. The Algaeof this sub-family are the narrowestand most delicate of the filamentousZygnemaceae. The thickness (3—41 yu,) ofthe filaments and relative length (2—35times the diameter) of the cells varybetween wide limits, and the cell-wall isrelatively thin. Each cell contains asingle chloroplast, usually in the form ofan axil
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . of conjugation. Of these theMesocarpese is the lowest group and theSpirogyreas the most advanced. Sub-family MESOCARPETE. The Algaeof this sub-family are the narrowestand most delicate of the filamentousZygnemaceae. The thickness (3—41 yu,) ofthe filaments and relative length (2—35times the diameter) of the cells varybetween wide limits, and the cell-wall isrelatively thin. Each cell contains asingle chloroplast, usually in the form ofan axile plate (fig. 210 A and £), whichmay extend from end to end of the cellor only occupy the median portion(fig. 209 D). The chloroplast contains from 2 to 14conspicuous pyrenoids, generally arrangedin a linear series. It is in some speciesof Debarya (D. desmidioides, fig. 213G—K; D. cruciata) that there are onlytwo pyrenoids, and in some of the thickerspecies of Mougeotia the pyrenoids aremore or less scattered (fig. 210 A). Thechloroplasts of adjacent cells usually liein the same plane, so that a whole filament of cells may present the full. Fig. 210. A and B, Motif/eotia sp., x500;A, cell showing the full face of thechloroplast; B, cell showing edge ofchloroplast. C and D, germination ofthe zygospore of Mougeotia parvula Hass.,x 390. E, germination of the zygosporeof M. laetevirens (A. Br.) Wittr., x , nucleus; p, pyrenoid. (C—E, afterDe Bary.) 336 Conjugate breadth of the chloroplasts or the filament may be in a position such thatonly the edge of the chloroplasts can be seen (fig. 210 J5). The action of light in causing the rotation of the plate-like chloroplasts of Mougeotiahas been known for a long time. In diffused daylight they place themselves at right-anglesto the direction of the incident rays, but the edge of the plate is directed towards strongsunlight. It was shown by Lewis (98) that the chloroplast occupies on an average30 minutes to rotate throu
Size: 1066px × 2344px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishercambridgeengtheuni
