. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . 34 Chlorophyceae lateral position. The rapid vibratile action of the cilia causes the zoogonidiumto swim quickly through the water, but the movements of some zoogonidiaare much more rapid than others. After a time (of variable length, butrarely more than an hour or two) the zoogonidium comes to rest, thecilia disappear, the protoplast secretes a cellulose wall, and the quiescent zoo-gonidium develops into a new plant (consult figs. 185 H—J; 1
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . 34 Chlorophyceae lateral position. The rapid vibratile action of the cilia causes the zoogonidiumto swim quickly through the water, but the movements of some zoogonidiaare much more rapid than others. After a time (of variable length, butrarely more than an hour or two) the zoogonidium comes to rest, thecilia disappear, the protoplast secretes a cellulose wall, and the quiescent zoo-gonidium develops into a new plant (consult figs. 185 H—J; 189 G). Manyzoogonidia on coming to rest attach themselves by their anterior colourlessextremity, which often develops into a hold-fast of greater or less complexity. Pascher (09) has found that in some of the Ulotrichales the swarm-sporesmay soon lose their cilia and then creep about in an amoeboid mannerfor half to three-quarters of an hour, after which they settle down andgerminate in the ordinary way. All zoogonidia must be regarded as homologous structures, and as will beemphasized in subsequent paragraphs they must also be considered as the. Fig. 91. A and B, Ulothrix idiospora G. S. West, showing scrobiculated akinetes (ak). C,a form of Zygnema ericetorum Kiitz., showing aplanospore (apt). D, chain of akinetes («A-)of Microspora floccosa (Vauch.) Thur. E, aplanospores (apl) of Microspora sp. [probablyM. abbreviata (Rabenh.) Lagerh.]. All x about 500. direct representatives of the vegetative individuals of the primitive motileforms which were derived from the Flagellata. In some groups (Protococcales, Ulotrichales, various Heterokontaj), singlenon-mobile gonidia are frequently produced from the vegetative cells. If thegonidium is formed by the rejuvenescence of the cell and the original cell-wall is retained as part of the final thick wall, the gonidium is said to bean akinete (fig. 91 A, B, and D). If, on the other hand, the rejuvenescenceresults in the formation
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