MYXOMYCETES AND SCHIZOPHYTES 205 



CYANOPHYCEAE. BLUE-GREEN ALGAE (Schizophyceae. Fission Algae) 



The blue-green algae include unicellular, colonial, and filamentous 

 forms. They occur everywhere in damp or wet places. On the vertical 

 faces of rocks where there is a constant dripping of water, brilliant 

 blue-green forms are abundant. In the Yellowstone National Park 

 the brilliant coloring of the rocks is due in large measure to members 

 of this group. Many forms occur as brownish or greenish gelatinous 

 layers on damp ground or upon rocks, or even upon damp wooden 

 structures in greenhouses. Other forms float freely in water or on the 

 surface of the water.. 



Oscillatoria. — For most purposes it is best to study Oscillatoria in 

 the living condition. It is readily found in watering-troughs, in stag- 

 nant water, on damp earth, and in other habitats. The commonest 

 forms have a deep blue-green or brownish color. It is very easy to keep 

 Oscillatoria all the year in the laboratory. Simply put a little of a de- 

 sirable form into a gallon glass jar half filled with water. By adding 

 water occasionally to compensate for evaporation, the culture should 

 keep indefinitely. In a jar with a tightly fitting cover we have kept 

 such a culture for years without renewing the water. 



For the purposes of identification and herbarium specimens the ma- 

 terial may simply be placed on a slip of mica and allowed to dry. 

 When wanted for use, add a drop of water and a cover, and the mount 

 is ready for examination. After the examination has been made, re- 

 move the cover, allow the preparation to dry, and then return it to the 

 herbarium. 



Good mounts may be made by the Venetian turpentine method. 

 Species of medium size are more satisfactory for a study of the nucleus 

 than the very large species. Fix in a chromo-acetic-osmic solution (1 g. 

 chromic acid, 3 c.c. acetic acid, and 7 c.c. 1 per cent osmic acid). Stain 

 in iron-alum haematoxylin, and follow the Venetian turpentine meth- 

 od. While the nuclei are easily seen in such preparations, still better 

 views can be secured from sections of paraffin material fixed in the 

 same solution or in Flemming's weaker solution. The section should 

 be 1-3 M thick. After staining with haematoxyhn, stain lightly with 

 orange dissolved in clove oil. In paraffin sections the scattered condi- 

 tion of the material as it appears in thin sections is very annoying. As 

 soon as the material is thoroughly washed in water, arrange it so that 

 the filaments will all have the same general direction. This will enable 

 you to get longitudinal and transverse sections. As you begin with the 



