156 Methods in Plant Histology 



movements like Oscillatoria, is often found in foul water. Its 

 presence may be indicated by whitish patches on the bottom. 



The Bacteria are the only plants in which a nucleus has not been 

 conclusively demonstrated, and some claim that a nucleus is present 

 even in Bacteria. In determining the presence or absence of a 

 nucleus in Bacteria, the crude method, just given, would be of no 

 value, and even the most critical methods of the bacteriologist, who 

 mounts the organisms whole, would be entitled to only scant con- 

 sideration. The presence or absence of a nucleus will have to be 

 determined by a study of thin, well-stained sections of perfectly 

 fixed material. 



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. 



Oscillatoria. For most purposes it is best to study Oscillatoria 

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

 stagnant water, on damp earth, and in other habitats. The com- 

 monest 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 desirable form into a gallon glass jar half filled with 

 water. By adding water occasionally to compensate for evapora- 

 tion, 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 

 material 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, 



