. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . 284 Ulotrichcdes Asexual reproduction takes place by aplanospores, akinetes and occur in a number of the smaller species of Ulothrix, in Uronemaand in Binuclearia (G. S. W., 04). They are more rarely found in thelarger Ulotlirix zonata (fig. 183 B and C). Wille (12) regards the aplano-spores of Stichococcus flaccidus, which are formed singly within the vegetativecells, as reduced zoogonidia; they germinate at once, div
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . 284 Ulotrichcdes Asexual reproduction takes place by aplanospores, akinetes and occur in a number of the smaller species of Ulothrix, in Uronemaand in Binuclearia (G. S. W., 04). They are more rarely found in thelarger Ulotlirix zonata (fig. 183 B and C). Wille (12) regards the aplano-spores of Stichococcus flaccidus, which are formed singly within the vegetativecells, as reduced zoogonidia; they germinate at once, dividing either cruciatelyor tetrahedrally, and ultimately form a palmella-state. A similar palmella-state may sometimes be observed in Ulothrix subtilis (G. S. W., 04). Insome instances they increase in size and become globular hypnospores withslightly asperulate walls. Akinetes are frequently formed in various speciesof Ulothrix, Stichococcus and Geminella. In Ulothrix idiospora G. 8. West (09)they are thick-walled and scrobiculate (fig. 91 A and B).. Fig. 181. Ulothrix zonata (Web. & Mohr) Kiitz. A, vegetative filament showing parietalring-like chloroplasts with pyreuoids (py). B and C, aplanospores. All x 800. Zoogonidia occur in Ulothrix, Stichococcus and Uronema. In Stichococcusthey are biciliated, but in Uronema they are quadriciliated; in both generaonly one zoogonidium arises from a mother-cell. In the genus Ulothrix, inwhich the different species range from 4 /j, in diameter (in the narrowestform of U. subtilis) to 70 fi (in the larger montane forms of U. zonata), thezoogonidia vary very much. From 1 to 32, or even more, may arise in amother-cell. In the narrower species they arise singly or less often inpairs, and are furnished with either two or four cilia. In the large speciesU. zonata, in which zoogonidium-formation was very carefully studied byDodel (76), every gradation in size is met with between macrozoogonidia Ulotrichaceae 285 with four cilia and microzoo
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