MYXOMYCETES AND SCHIZOPHYTES 
171 
aquatic plants. The nodules, when young, are firm like Nostoc , 
but as they grow older and larger they become hollow and soft. 
The older forms become so much dissociated that they lose their 
characteristic form and merely make the fixing fluid look turbid. 
Allow a drop of such material to spread out and dry upon a slide 
which has been slightly 
smeared with albumen 
fixative. Leave the 
slide in 95 per cent 
alcohol 2 or 3 minutes 
to coagulate the albu¬ 
men fixative, and then 
stain in safranin. If 
the background ap¬ 
pears untidy, stain for 
24 hours, or longer; 
you can then extract 
the stain from the 
background, and still 
leave the long spore 
and some of the other 
features of the fila¬ 
ment well stained. A 
touch of cyanin will 
bring out the sheath. 
Cyanin and erythro- 
sin is a good combina¬ 
tion if the material 
is clean. The firmer nodules may be treated like Nostoc or Rivularia. 
Wasserbliithe.—Many genera of the Cyanophyceae occur as 
scums, often iridescent, on the surface of stagnant or quiet water. 
Some of the commonest forms are Coelosphaerium and Anabaena 
(Fig. 35). Some of the Chlorophyceae also occur as Wasserbliithe. 
Where the material is very abundant, it may be collected by simply 
skimming it off with a wide-mouthed bottle, but where it is rather 
scarce, it is better to filter the water through bolting silk and finally 
rinse the algae off into a bottle, adding enough formalin to the water 
in the bottle to make a 5 per cent solution. The material may be 
kept here indefinitely, but after a few hours it is ready for use. If 
Fig. 34.— Gloeotrichia: photomicrograph from a preparation 
stained in cyanin and erythrosin: negative by Dr. W. J. G. Land. 
