CHAPTER XIX 



RHODOPHYCEAE. RED ALGAE 



The red algae belong almost exclusively to salt water, but a few 

 genera are found only in fresh water, usually in running water, and a 

 few forms occur both in salt and in fresh water. Nearly all are small 

 forms, and for habit work can be floated out and mounted on paper. 

 A few, like Chondrus crispus, will need glue or gummed paper. When 

 the floating out is carefully done, the small, filamentous forms, com- 

 monly called sea mosses, make beautiful place cards and decorations 

 for letterheads, as well as serviceable herbarium specimens. The first 

 day, the blotters should be changed three times; twice, the second day; 

 and once a day thereafter until the specimens are perfectly dry. This 

 may seem unnecessarily laborious, but specimens prepared in this way 

 keep indefinitely all the brilliancy of their natural colors. 



For more critical habit work and for Venetian turpentine mounts, 

 fix in 6-10 per cent formalin in sea water. Just a trace of acetic acid 

 will improve it, and the stock of material for future use will keep bet- 

 ter. For the red algae, keep a 1 per cent solution of acetic acid (1 c.c. 

 glacial acetic acid in 100 c.c. sea water). To the 10 per cent formalin 

 add 5 c.c. of this weak acetic acid to 100 c.c. of the formalin solution. 



For nuclear detail, material must be imbedded in paraffin. Chromo- 

 acetic-osmic is the best fixing agent. The following is a good formula to 

 begin wuth and is not likely to need much modification : 



Chromic acid . 7 c.c. 



Glacial acetic acid 3 c.c. 



Osmic acid 7 c.c. 



Water 90 c.c. 



Always add the osmic acid just before fixing. 



In this solTition, many of the delicate red algae fix with amazing 

 rapidity. For Ceramium rubrum, 1-2 seconds is enough. Even if the 

 material does not break up in the fixing agent, if fixed too long, it will 

 go to pieces in the 50 or 70 per cent alcohol. For Polysiphonia, 5-40 

 seconds is about right. If the time is too prolonged, the material is 

 likely to break up in the fixing agent. For many forms of similar con- 



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