. The causes and course of organic evolution; . and a storing area for energizing food material. The cyanophyceous organisms probably originated frommore primitive bacterial ancestors first in thermal fresh-waterareas, and at temperatures of 75-50° C. We have acceptedit that 41 existing species which still live under such conditionsare probable direct descendants of these. By acclimatizationto cooling terrestrial conditions in fresh-water, on moist sur-faces, or in shady moist places, and later in the sea, a wealthof species probably evolved during mid-archsean times thatbecame the ancestors o
. The causes and course of organic evolution; . and a storing area for energizing food material. The cyanophyceous organisms probably originated frommore primitive bacterial ancestors first in thermal fresh-waterareas, and at temperatures of 75-50° C. We have acceptedit that 41 existing species which still live under such conditionsare probable direct descendants of these. By acclimatizationto cooling terrestrial conditions in fresh-water, on moist sur-faces, or in shady moist places, and later in the sea, a wealthof species probably evolved during mid-archsean times thatbecame the ancestors of all green plants, while the prepon-derating wealth of species now living in fresh-water or moistland areas, as compared with the much smaller number ofmarine species, seems to be a correct index to their primitiveenvironment. From green or reddish green unicellular Cyanophycese wehave traced what are probably the simplest nucleate greenalgae hke Pleurococcus and Tetrasporay while from olive-green11 322 Causes and Course of Organic Evolution. —Statues in evolution of the asexual and sexual generations in RedSeaweeds. 1, Bangia alropurparea; 2, Lemanea torulosa; 3, Chantransia sp.,4, Batrachospermwn; 5, Nemalion, 6, Dudresnaija; 7, Rhodomela (afterFalkenberg); Ic Chondria (after Bornet). \m. 3m., nionospore, 6, a, tetra-spore; h, female apparatus with carpogone cell bearing trichogyne (/r);/>,spermatium; cc, earlier and later stages in formation of carpospores from fer-tilized carpogone cells. Evolution of Plants 323 or bright green unicellular members of the same division theDesmidese and higher green Conjugatse probably sprang, andthese have practically all retained a fresh-water protococcaceous ancestors we have derived the Vol-vocacese that are fresh-water and also represent the climaxof unicellular specialization. From some simple unicellulargreenish brown fresh-water genus like Amphidiniiim, derivedin turn from pleurococcaceous ancestry, the
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