. Botany; principles and problems. Botany. THE THALLOPHYTA 283 point already well up in the scale of algal evolution. The higher members of the class display an unquestionable alternation of generations. Two typical genera will illustrate the complexities of reproduction in this group. Nemalion (Fig. 160) is a common form with a branching, filamentous habit and represents the simplest of the red algae. The numerous small antheridia profluce non-motile,. Fig. 161.—Polysiphonia fihrillosa. A, Portion of a tetrasporic plant showing three groups of tetraspores. These spores occur in tetrads or gro
. Botany; principles and problems. Botany. THE THALLOPHYTA 283 point already well up in the scale of algal evolution. The higher members of the class display an unquestionable alternation of generations. Two typical genera will illustrate the complexities of reproduction in this group. Nemalion (Fig. 160) is a common form with a branching, filamentous habit and represents the simplest of the red algae. The numerous small antheridia profluce non-motile,. Fig. 161.—Polysiphonia fihrillosa. A, Portion of a tetrasporic plant showing three groups of tetraspores. These spores occur in tetrads or groups of four. X 90. B, portion of a male plant. Above, an immature antheridium; below, a mature one, producing large numbers of sperms on its surface. X 215. C, portion of a female plant showing a ripe cystocarp, its wall enclosing a group of carpospores. X 45. binucleate sperms. The female sexual organ, which is here called the procarp, consists of two cells—a basal carpogonium, containing the single female cell and homologous with the oogo- nium of other algae; and a terminal cell, the trichogtjne, which is drawn out into a hairlike tip. The sperm is carried bj^ water currents to the trichogyne, down which its contents passes into the carpogonium. The fertilized carpogonium does not develop a new plant directly, but produces a group of short filaments on the end of each of which is borne a non-motile carpospore. This whole structure of spores, filaments, and carpogonium is known as the cystocarp. A carpospore germinates directly into a new plant. Polysiphonia (Fig. 161), another common member of tli(> class, displays a much more complex sexual history and is tyj^ical of. 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 Sinnott, Edmund Ware, 1888-. New York, McGraw-Hill
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1923
