Probably no algae has been more studied by pupils, teachers, and investigators than Spirogyra. Nearly all of the numerous species belong to the low, quiet waters of ponds and ditches, where they often form large, flocculent green mats nearly covering the surface of the water. A few species occur in running water. The mats are very slippery to the touch-a character which assists in recognizing the genus in the field. In the larger species the characteristic spiral chromatophores can be seen with a good pocket lens, thus completing the identification, as far as the genus is concerned. Mats in which zygospores have been formed are likely to show a pale, or even a brownish, color, due to the brownish walls of the zygospores. This color, however, is not always, or even usually, due to zygospores, but is more often due to the death and degeneration of the plants. Mats in early stages of conjugation and those with young zygospores show as bright a green as vigorously growing material.
Spirogyra is not easy to keep in the laboratory. The small species keep better than the larger ones. Put only a small amount of the material in a jar and use rain water. If it is necessary to use tap water, let the water run for a minute before taking the water for the culture. Most metals are poisonous to Spirogyra, even the small amount taken up by the water while standing in the water pipe being detrimental.
The species found in running water will usually conjugate within a week when brought into the laboratory and placed in rain water or tap water. Species belonging to quiet waters, when brought into the laboratory and placed in a 0.2 per cent Knop's solution, are likely to undergo rapid cell division and growth. After the alga has remained in such a culture for a few days or for a week, conjugation may be induced by transferring to rain water or tap water, and keeping the culture in bright sunlight. Conjugation may begin within 3 or 4 days. Variations in temperature between 1 and 15 C. have little influence upon conjugation.
The special chromo-acetic-osmic solution fixes well. Stain some material in iron-alum haematoxylin and some in Magdala red and anilin blue. Use the Venetian turpentine method, and on each slide mount material stained in both ways. With Magdala red and anilin blue the spiral chromatophore takes the blue and its pyrenoids the red. If the material contains figures, stain in iron-haematoxylin. This will stain the figures, but will hardly touch the chromatophore or cell wall, thus allowing an unobstructed view of the figures. While figures occur occasionally in the daytime, collect your material at night, preferably near midnight.
Spirogyra is easily imbedded and cut.
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