Chlorophyceae 169 



Ulothrix. Where the problem of the origin and evolution of sex 

 is studied, Ulothrix is an indispensable type. Ulothrix zonata is 

 found in springs, brooks, and rivers, occurring in bright-green masses 

 attached to stones in riffles, especially in sunny places. It is abun- 

 dant on stones and piles along the beaches of lakes. 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. 



While the most instructive study demands living material, 

 some details are more easily seen in stained preparations. Fix in 

 chromo-acetic acid and use the Venetian turpentine method. Stain 

 in iron-alum haematoxylin. It is a good plan to stain some of the 

 material in Magdala red and anilin blue. When mounting, some 

 material from each lot can be used for every preparation. The 

 iron-haematoxylin will give the best views of the nucleus; the anilin 

 blue will stain the chromatophore and cell well. In general, it is a 

 good plan to put upon the same slide material prepared in various 

 ways. A single preparation will then afford a rather complete study. 



Oedogonium.--This form is attached when young, but most 

 species float freely when they are older. Most species are found 

 in quiet waters, especially in ponds and ditches. The floating 

 masses bear some resemblance to Spirogyra, but are not so slippery. 

 The best fruiting material is often found attached to twigs, rushes, 

 and various plants, where, to the naked eye, it forms only a fuzzy 

 covering rather than a dense mat. 



In studying Oedogonium diplandrum, Klebs found that a change 

 from a lower to a higher temperature would induce the production 

 of zoospores. A culture which had been kept in a cold room with 

 a temperature varying from 6 to C., when brought into a warmer 

 room with a temperature varying from 12 to 16 C., produced an 



