. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 817. from difierent gamete-producing organs {gametangia), and in Dasy- dadus, only between gametes from different plants, though it is impossible in any of these to distinguish male and female characters. However, in the Conjugales, one of the gametes often is immotile, while the other migrates from a neighboring filament through a passageway made by the fusion (or conjugation) of two lateral outgrowths (figs. 107-109). From analogy with the higher plants, the immotile gamete may be called female and th
. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 817. from difierent gamete-producing organs {gametangia), and in Dasy- dadus, only between gametes from different plants, though it is impossible in any of these to distinguish male and female characters. However, in the Conjugales, one of the gametes often is immotile, while the other migrates from a neighboring filament through a passageway made by the fusion (or conjugation) of two lateral outgrowths (figs. 107-109). From analogy with the higher plants, the immotile gamete may be called female and the motile gamete, male. In some conjugating forms, as Mucor, there is no such distinction, the two gametes moving equally and meeting in the passageway between the filaments (figs. 163- 166). Usually zygospores are thick-walled rest- ing cells closely packed with food and well able to exist over severe periods (figs. 50, no, 166). Heterogamy. — In the great majority of plants, including many thallophytes and all the higher plants, the two gametes are unequal; this con- dition is known as heterogamy, and the spore re- sulting from the fusion of unequal gametes is called an oospore. It is in the heterogamous plants that one may speak of true sex differenti- ation and of the development of male gametes or sperms and of female gametes or eggs (fig. 1135). In nearly all bryophytes, pteridophytes, and heterogamous algae the sperms are relatively small, ciliated, actively motile bodies (figs. 28, 119, 320, 349, 415), whereas in the seed plants (except in Ginkgo and in the cycads, fig. 455), they are non-ciliated, and exhibit but little true locomotion (fig. 479). Eggs commonly are much larger than,sperms, and, except in the case of a few algae where they float freely in the water, they are essentially immotile (figs. 31, 77, 481). Often the male and female gametes are borne in special organs, the antheridia and the oogonia (or archegonia), respectively. In many thallophytes the oospo
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