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METHODS IN PLANT HISTOLOGY 
Leptothrix may often be obtained by scraping the inside of the 
cheek. Beggiatoa, one of the sulphur bacteria, with oscillating 
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 considera¬ 
tion. 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 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 
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 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 
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 
remove the cover, allow the preparation to dry, and then return it 
to the herbarium. 
