. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. THALLOPHYTA, 673 Alliance XV.—Zygomycetes. Families: MucoracecB, Mortierellece. Are mould-like saprophytes with a much-branched, non-septate mycelium; sexual reproduction by conjugation; swarm-spores never met with. I'he com- mon Mucor Mucedo (fig. 384) may be regarded as typical of this group. Its mycelium establishes itself on the substratum, and develops long-stalked sporangia at various points on its sur- face (fig. 3841). In each sporangium (fig. 384 2) numer- ous spores are contained, and these
. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. THALLOPHYTA, 673 Alliance XV.—Zygomycetes. Families: MucoracecB, Mortierellece. Are mould-like saprophytes with a much-branched, non-septate mycelium; sexual reproduction by conjugation; swarm-spores never met with. I'he com- mon Mucor Mucedo (fig. 384) may be regarded as typical of this group. Its mycelium establishes itself on the substratum, and develops long-stalked sporangia at various points on its sur- face (fig. 3841). In each sporangium (fig. 384 2) numer- ous spores are contained, and these can germinate, producing new mycelia on a suitable substratum. A conjugation of branches of the mycelium leading to the production of a fruit or zygospore (fig. 384 ^) occasionally takes place, but the sexual method of repro- duction is much commoner in other members of the group (of. pp. 53, 54). The zygospore (or zygote) is invested in a strongly thickened membrane and can remain dormant for a considerable period. The hyphse in many of the Mucors can break up into continuous chains of cells which disarticu- late and propagate the plant; these oflfshoots are known as chlamydospores or gemmae. It often happens amongst the Mucors that although the conjugating branches are produced, they do not conjugate but each produces a fruit parthenogenetically. These, in contradistinction to zygospores, are called " azygospores". Or, as in Mucor tenuis, the "conjugating branches" no longer arise in pairs but isolated; these also form azygospores. Thus in this group, as in the Saprolegniacijse of the alliance Oomycetes, we note a tendency for sexuality to become obsolete (cf. p. 670). A good deal of variety exists in the Mucoracese in the arrangement of the sporangia. In Thamnidium the sporangial branch ends in a large sporangium, and in addition bears laterally a number of tiny sporangia (sporangioles) containing four spores each,, whilst in Chostocladium there is a f
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
