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DK HORATIO WOOD'S METHOD FOR PRESERVING 

 FRIiSH WATER ALG^E.* 



There are three or four distinct classes of localities, in each of 

 which a different set of forms may be looked for. These are 

 stagnant ditches and pools, springs, rivulets, large rivers, and other 

 bodies of pure water, dripping rocks in ravines, &c. ; trunks of 

 old trees, boards, branches and twigs of living trees, and other 

 localities. 



In regard to the first — stagnant waters — in these the most con- 

 spicuous forms are Oscillatoria? and Zygnemacefe. The Oscilla- 

 torias may almost always be recognised at once by their forming 

 dense slimy strata, floating or attached, generally with very fine 

 rays extending from the mass, like a long, delicate fringe. The 

 stratum is rarely of a bright green colour, but is mostly dark, dull 

 greenish, blackish, purplish, blue, &c. The Oscillatoria? are equally 

 valuable as specimens at all times and seasons, as their fruit is not 

 known, and the characters defining the species do not depend upon 

 sexual organs. The Zygnemas are the bright green, evidently 

 filamentous, slimy masses, which float on ditches, or lie in them, 

 entangled amongst the water plants, sticks, twigs, &c. They are 

 only of scientific value when in fruit, as it is only at such times 

 that they can be determined. Excepting in the case of one or two 

 very large forms, it is impossible to tell with the naked eye with 

 certainty whether a Zygnema is in fruit or not ; but there are one 

 or two practical points, the remembrance of which will very greatly 

 enhance the probable yield of an afternoon's search. In the first 

 place the fruiting season is in the spring and early summer, the 

 latter part of March, May, and June being the months when 

 the collector will be best repaid for looking for this family. Again, 

 when these plants are fruiting they lose their bright green colour 

 and become dingy, often yellowish, and very dirty looking — just 

 such specimens as the tyro would pass by. The fine, bright green, 

 handsome masses of these algse are rarely worth carrying home. 

 After all, however, much must be left to chance ; the best way is to 

 gather small quantities from numerous localities, keeping them 

 separate until they can be examined. . 



Adhering to the various larger plants, to floating matters, twigs, 

 stones, &c, in ditches, will often be found filamentous Algas, which 

 make fine filmy fringes around the stems, or on the edges of the 

 leaves, or perchance one may meet with Rivalariae or Nostocs, &c, 

 forming little green or brownish balls, or indefinite protuberances 

 attached to small stems or leaves. These latter forms are to be 

 looked for, especially late in the season, and whenever seen should 

 be secured. 



In the latter part of summer there is often a brownish, gelatinous 



* Extracted from "A Contribution to the Natural History of the Fresh Water 

 Algse of America." Washington, 1873. 



