. Fresh-water biology. Freshwater biology. THE FRESH-WATER ALGAE 127 8 (6, 7) Valves circular, with radial rows of dots, between which are clear spaces; center either punctate or hyaline; on the margin a circle of acute spines; girdle view with undulating ends. Stephanodiscus Ehrenberg. The length of the spines on the margins of the cells varies greatly: in some species they are short and acute, while in others they may exceed the diameter of the cell many times. Stephanodiscus occurs frequently in the plank- ton, but usually not in great Fig. 73. Stephanodiscus niasareoe Ehrenber
. Fresh-water biology. Freshwater biology. THE FRESH-WATER ALGAE 127 8 (6, 7) Valves circular, with radial rows of dots, between which are clear spaces; center either punctate or hyaline; on the margin a circle of acute spines; girdle view with undulating ends. Stephanodiscus Ehrenberg. The length of the spines on the margins of the cells varies greatly: in some species they are short and acute, while in others they may exceed the diameter of the cell many times. Stephanodiscus occurs frequently in the plank- ton, but usually not in great Fig. 73. Stephanodiscus niasareoe Ehrenberg. X 606. (Original.) A B 9 (i, 10) Valves more or less cylindrical, often in chains, ends greatly ex- tended, usually forming long spines. Family RmzosoLENlACEAE. Only one genus Rhizosolenia Ehrenberg. Fig. 74. Rhizosolenia eriensis H. Smith. Schroter.) X 190. (After 10 (i, 9) Valves not circular or cylindrical, of different shapes, symmetrical in reference to a longitudinal or transverse axis; surface marked by costae or ptmctate lines making definite angles with a middle raphe or a median Une 11 11(34,38) A middle nodule present on the raphe of both valves. ... 12 See also 40 and 65. 12 (32, 36) Girdle view symmetrical with reference to both a transverse and a longitudinal axis 13 13 (26) Valves not arched or keeled; usually symmetrical with reference to a straight or a sigmoid raphe. Family Naviculaceae . 14 Valves symmetrical with reference to a straight or curved middle line; girdle symmetrical with reference to both axes; a straight or curved raphe; a central and two end nodules present. 14 (is) Cells without inner partitions; raphe and valves straight. ... 16 15(14) Raphe and valves sigmoid Pleurosigma W. Sm\\ Fig. 75. Fleurosigma attenuatum W. Smith. X 300. (After Smith.) 16 (19) Cells linear, oblong, with rounded nodules, the two end ones turned toward one side, the prominent costae not 17 17 (18) The costae interrupted by a plain band at the center. Sta
Size: 2274px × 1099px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
