. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . hot springs, and have beenobtained in a living state at a temperature of certainly as high as 55° C. Somespecies are cosmopolitan, occurring in all parts of the world, but there are onthe contrary many species and genera which occur only in certain seas andclimates. The same is true to a lesser extent of freshwater forms, and whenthese forms are more fully and accurately investigated from a systematicpoint of view, many marked geographical pe
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . hot springs, and have beenobtained in a living state at a temperature of certainly as high as 55° C. Somespecies are cosmopolitan, occurring in all parts of the world, but there are onthe contrary many species and genera which occur only in certain seas andclimates. The same is true to a lesser extent of freshwater forms, and whenthese forms are more fully and accurately investigated from a systematicpoint of view, many marked geographical peculiarities will doubtless bebrought to light. The free and unattached diatoms often form a yellow-brown scum at thesurface of the water or on the sediment at the bottom of shallow also occur in abundance among the leaves of aquatic phanerogamsor among the branches of larger alga3. Many species are epiphytic, beingattached to the thallus of larger algse. In fresh waters the filaments ofvarious species of Cladophora, Rhizoclonium, and Vaucheria are frequentlythickly covered with Cocconeis Placentula or C. Pediculus (fig. 84), and often. Fig. 84. A small portion of a tilament of Rhizoclonium hieroi/lyphicinn Kiitz. largely coveredwith the epiphytic diatom Cocconeis Pediculus Ehrenb. x 375. Only the outlines of thecells are shown. with Epithemia turgida. Several minute species of Achnanthes are alsoepiphytes of this nature. In the sea the genera Isthmia, Grammatophora,Rhabdonema, Licmophora, and others are epiphytes on the smaller diatoms pass the whole of their existence free-floating in thesurface-waters of the sea, or of lakes and large rivers. These are the plankton-diatoms which occur in prodigious quantity in the cold waters of the Arctic andAntarctic Oceans, and to a lesser degree in the warmer oceans. The marineplankton-diatoms are almost exclusively centric, and some of the principalgenera are Ch&toceras, Biddulphia, Thalassiosira, Cosc
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