. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . This beak-like part of the protoplast is stated byStrasburger to consist of kinoplasm. Each zoogonidium may possess oneor more chloroplasts, and is frequently provided with two minute contractilevacuoles situated in front of the nucleus close to the anterior red pigment-spot (or stigma) is often present, usually in an anterior and 1 In the genus Vaucheria the single large zoogonidium is a compound structure which mayin all probabi
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . This beak-like part of the protoplast is stated byStrasburger to consist of kinoplasm. Each zoogonidium may possess oneor more chloroplasts, and is frequently provided with two minute contractilevacuoles situated in front of the nucleus close to the anterior red pigment-spot (or stigma) is often present, usually in an anterior and 1 In the genus Vaucheria the single large zoogonidium is a compound structure which mayin all probability be regarded as representing the fusion of a large number of small biciliatedzoogonidia such as are typical of the Isokontee. 2 The zoogonidia of certain Algte belonging to the Heterokontas have been described aspossessing only one cilium, but in those cases in which the zoogonidia have been carefullyre-examined the second, much shorter, cilium has been - 134 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
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