A treatise on the British freshwater algæ / by G. S. West.

  • George Stephen West
Date:
1904
Catalogue details

Licence: In copyright

Credit: A treatise on the British freshwater algæ / by G. S. West. Source: Wellcome Collection.

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    Freshwater Algai Class 4. Heterokontce (or the Yellow-green Algae), contain- ing a large proportion of a yellow pigment known as xanthophyll. The stored product of assimila- tion is a fatty substance. Freshwater. Class 5. Bacillariece (or the Diatoms), containing a brown colouring-matter diatomin, which much resembles the phycophaein of the brown Algae. Universal both in fresh and salt water. Class 6. Myxophycece (or the Blue-green Algae), containing a blue colouring-matter known as phycocyanin. The stored product of assimilation is most probably glycogen. Mostly freshwater. By far the greater part of the vegetation of the sea consists of marine Algae, and with few exceptions these marine forms are of quite a different nature from the freshwater ones. It is only with freshwater Algae that this volume is concerned. Certain Algae are known in a fossil state. These are mostly Diatoms, the siliceous valves of which are eminently suited for fossilization, and a few others in which the thallus was encrusted with carbonate of lime. The majority of other Algae are of much too fragile and delicate a nature to become fossilized, and most of the records of such fossil Algae are of very doubtful value. Freshwater Algae exhibit a variety of types of structure. Some of them are unicellular, each plant consisting of a single protoplasmic unit or energid (i.e. a mass of protoplasm containing a single nucleus) surrounded and enclosed by a definite cell-wall (e.g. Desmidiaceae, Bacillarieae, and many Protococcoideae); others are unseptate or coenocytic plants composed of an aggregate of protoplasmic units enclosed within a common cell-wall (e.g. Sipho- neae, Hydrodictyon); others are incompletely septate plants, each segment containing a number of protoplasmic units within a cell- wall, the septation of the plant going on independently of the divisions of the nuclei (e.g. Cladophorales); others are multi- cellular or completely septate plants, each segment containing one protoplasmic unit (e.g. Zygnemaceae, Chaetophorales, etc.). Many of the unicellular forms are solitary cells, but others occur as colonies, in which the individual cells are more or less loosely held together in a common mucilaginous envelope, which is either secreted by the protoplasm of the cells or is derived from
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