What are ulothrix?

Where the problem of the origin and evolution of sex is studied, Ulothrix is an indispensable type. Ulothrix sonata is found in springs, brooks, and rivers, occurring in bright-green masses attached to stones in riffles, especially in sunny places. It is abundant on stones and piles along the beaches of lakes. Nuclear division takes place at night, most abundantly about midnight, and is followed by a rapid development of zoospores and gametes, which continue to be discharged throughout the forenoon. In the afternoon the material is largely vegetative. Another species is found in stagnant ponds, ditches, and even in watering-troughs and rain-barrels. It is difficult to keep in the laboratory the forms which are found, in rapidly flowing water. However, if they are brought in still attached to stones and placed under a stream of tap water, they may live for a couple of weeks and may produce zoospores every morning. The production of zoospores may continue for a few days, if the material is merely put into a jar of water; in a 2 to 4 per cent cane-sugar solution the production of zoospores continues a little longer.

No form is better than Ulothrix for illustrating to a class the difference between zoospores and gametes. Even when gametes are not conjugating, their more rapid movement is noticeable; and when conjugating, the awkward, jerky movements of the pair contrasts sharply with the graceful movements of the zoospores.

Fix in the special chromo-acetic-osmic solution and stain some material in iron-alum haematoxylin, which will differentiate the nuclei and pyrenoids; and stain some in Magdala red and anilin blue, which is better for the cell wall and chromatophore. Mount on each slide material from both lots, and the preparation will then afford a rather complete study.

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