. Fundamentals of botany. Botany. LIFE HISTORIES OF ALG^ 247 to as tetrasporic plants. When the tetraspores are set free they soon become attached to some solid object, and, like the fertihzed eggs, develop into plants that externally resemble, at- maturity, those bearing tetraspores. Thus, the plants produced by the fertilized eggs and by the tetra- spores closely resemble each other in all vegetative characters; they differ externally only in the kind of reproductive organs they bear. 233. Alternation of Generations.âAlthough the Dic- tyota plants developed from zygotes and spores look alike
. Fundamentals of botany. Botany. LIFE HISTORIES OF ALG^ 247 to as tetrasporic plants. When the tetraspores are set free they soon become attached to some solid object, and, like the fertihzed eggs, develop into plants that externally resemble, at- maturity, those bearing tetraspores. Thus, the plants produced by the fertilized eggs and by the tetra- spores closely resemble each other in all vegetative characters; they differ externally only in the kind of reproductive organs they bear. 233. Alternation of Generations.âAlthough the Dic- tyota plants developed from zygotes and spores look alike, 'vSS>-. ,j(S2J ../r ;. C I aâ '"::% ^^.>---:^^ \; \-- .-â â - V -.,-- f -^^ - C ' '*''V '=.rk^ Fig. 182.âDictyola dichotoma. A, Vertical section, transverse to the axis of tlie thallus, showing a polar view of the nuclear plate in the first division of the antheridium. C, Similar view of the first division of the oogonium; B, similar view of the first nuclear division of the fertilized egg. Note that the reduced (haploid) number of chromosomes in A and C is 16, while the fertilized egg (B) shows the diploid number (32). (Redrawn from J. Lloyd Williams.) it is obvious that the products of the tetraspore, since they bear gametes, and never spores, are gametophytes; and the products of the fertilized egg, since they bear spores only, and never gametes, are sporophytes. These facts have only recently been established by careful experi- mental cultures. There is thus a true alternation of generations, although, in marked contrast to the ferns and mosses, the plant bodies of the two generationsare. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gager, C. Stuart (Charles Stuart), 1872-1943. Philadelphia, P. Blakiston's son & co.
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