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Freshwater Algæ.[1]
By A. W. Wills, F.C.S.
The objects of the "Midland Naturalist" are, like those of the several societies in the Union which it represents, at least threefold, viz.:—1st, to record such original researches and observations as their members may be fortunate enough to make; 2nd, to facilitate a complete a record of the flora and faunas of the several districts of the Midland Counties; and lastly, to enable lovers of Natural History to hold out a helping hand to one another by pointing out how others may pursue most profitably such branches of study as they have themselves specially affected, and by communications to one another such hints as are derived from their individual experience, whereby success may be ensured, time saved, or gaps in special lines of investigation filled up.
The present paper fails within the scope of the last division; it records little or nothing which is original; its object is to invite attention to a branch of microscopical study in which there is ample scope for observation, and to point out in what fashion the examination of the great group of plants known as the Freshwater Algæ may be successfully begun and carried on.
In doing this it will be convenient to ask and briefly to answer the following questions:—What are Freshwater Algæ, and why will they repay patient investigation? Where must they be sought? What are the general features of their stricture, modes of reproduction and morphology, and the characteristics of the principal groups into which they are divided? How are they best collected and preserve? And how should observations be recorded?
1st—Freshwater Algæ are minute plants, mostly requiring considerable magnifying power to reveal their structure, belonging to that great group of waterweeds included in the somewhat loose term of Confervoidoæ or Chloraspermeæ, of which the coarser green weeds of the sea shore are the most familiar examples.
The imperfection of a classification by reference to the colony of these plants or of their spores will become evident from the outset; it must be accepted only as a rough division by which the majority only of the genera are covered.
The freshwater species are far more delicate in texture and various in form than the marine ones, and comprise, in addition to those larger
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Description of Figures.—Plate I.
Fig. 1.—Chlorococcum vulgare, from the bark of an ash tree, showing subdivision of cells info groups of two, four, &c.
Fig. 2.—Protococcus—Species allied to P. pluvialis, from a freshwater aquarium, showing subdivision of cells and formation of motile forms.
Fig. 3.—Urococcus sp? Hass., from damp wall of a greenhouse.
Fig. 4.—Protococcus sp?, from wet rocks at Church Stretton.
Fig. 5.—Tetraspora tubrica, from bogs in Sutton Park.
Fig. 6.—Micrasterias rotula and Cosmarium cœlatum, from bogs in Sutton Park, showing increase by cell-division.