. Botany of the living plant. Botany. m BOTANY OF THE LIVING PLANT repeated divisions to form short discoid cells, which are the antheridia. Each, on opening in the same way, sets free two spermatozoids, the result of division of its protoplast. They resemble the zoospores in form, but are smaller. In some species special small plants (dwarf- males) are produced from smaft zoospores, which fix themselves in the neighbourhood of the oogonium, and dividing into a few cells, liberate their spermatozoids close to the opening (Fig. 331, C, D). Fertilisa- tion follows by fusion of the spermatozoid a
. Botany of the living plant. Botany. m BOTANY OF THE LIVING PLANT repeated divisions to form short discoid cells, which are the antheridia. Each, on opening in the same way, sets free two spermatozoids, the result of division of its protoplast. They resemble the zoospores in form, but are smaller. In some species special small plants (dwarf- males) are produced from smaft zoospores, which fix themselves in the neighbourhood of the oogonium, and dividing into a few cells, liberate their spermatozoids close to the opening (Fig. 331, C, D). Fertilisa- tion follows by fusion of the spermatozoid at the receptive spot of the ovum, and the coalescence of the nuclei has been observed. The zygote formaS a firm pro- tective wall: it is stored with nutriment, takes a brown or red colour, and may enter a period of rest. Its germination presents a point of special interest. The outer wall bursts and the contents escape, contained within a delicate membrane. The protoplast then divides usually into four cells, which ultimately escape as motile zoospores (Fig. 332). This division into four, following on sexual fusion, suggests a process of reduction comparable to that seen in the tetraspores of Polysiphonia or Dictyota, or in the spore-mother-cells of Mosses and But it is stated that the zygote may occasionally germinate. Fig. 332. Bulbuchaete intermedia. A -^oospore. B = formation of four zoospores in the gerimnating oospore. (After Pringsheim, from Strasbur- ger.) ( X 250.) without those divisions, to form a new individual directly, while an unfertilised oogonium may do the same. It would thus appear that the cycle of events is not so stereotyped here as it has become in more advanced plants. SiPHONALES. The Siphonales have already been discussed in Chapter IX., in respect of their pecuhar structure (p. 139, Fig. 98). They are coenocytes : that is, they are not partitioned into separate cells, but the plant-body consists of a large non-septate sac, limited by a cell-wall, and k
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