. The algae. Algae. Fig. 80 Dictyota dichotoma. A, portion of plant showing regular dichotomy. B, apical cell. C, apical cell divided. D, group of antheridia surrounded by sterile cells. E, single antheridial cell and a sterile cell. F, sorus of oogonia. G, tetrasporangium. (A-D, F, G, after Oltmanns; E, after Williams.) the formation of an antheridium a superficial cell divides into a stalk cell and an antheridium initial, the final partition of the an- theridium initial into the individual antheridial mother cells taking place only a few days before the antherozoids are to be liberated. The
. The algae. Algae. Fig. 80 Dictyota dichotoma. A, portion of plant showing regular dichotomy. B, apical cell. C, apical cell divided. D, group of antheridia surrounded by sterile cells. E, single antheridial cell and a sterile cell. F, sorus of oogonia. G, tetrasporangium. (A-D, F, G, after Oltmanns; E, after Williams.) the formation of an antheridium a superficial cell divides into a stalk cell and an antheridium initial, the final partition of the an- theridium initial into the individual antheridial mother cells taking place only a few days before the antherozoids are to be liberated. The mature antherozoid is pear-shaped with only one cilium, and as each plurilocular antheridium liberates about 1,500 anthero- zoids, a single sorus may generate as many as 450,000. The number of ova produced is not so numerous, and it has been estimated that there are about 6,000 antherozoids available for each ovum. The oogonial sorus is very similar to the antheridial sorus, the large fertile oogonia, twenty-five to fifty in ntmiber, being situated in the centre and surrounded by sterile cells on the outside. The oogonia likewise arise from superficial cells that divide into a stalk cell and oogonium initial, and each oogonium when ripe produces one ovum. Liberation of both kinds of gamete usually commences from the centre of a sorus and fertihzation takes place in the water, but during the process the eggs are not caused to revolve by the activities of the antherozoids as they are in Fucus (cf. p. 202). If the process is followed under a microscope it can be noted that only some of the eggs appear capable of attracting antherozoids. Unfertilized ova may develop parthenogenetically; such plants, 146. 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 Chapman, V. J. (Valentine Jackson), 1910-. London, Macmillan;
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