208 



METHODS IN PLANT HISTOLOGY 



slightly smeared with albumen fixative. Leave the sHde in 95 per cent 

 alcohol 2 or 3 minutes to coagulate the albumen fixative, and then 



stain in safranin. If the 

 background appears 

 untidy, stain for 24 

 hours, or longer; you 

 can then extract the 

 stain from the back- 

 ground, and still leave 

 the long spore and 

 some of the other fea- 

 tures of the filament 

 well stained. A touch 

 of light green will bring 

 out the sheath. Iron- 

 alum haematoxylin, 

 followed by orange in 

 clove oil, gives a beau- 

 tiful differentiation. 

 The firmer young nod- 

 ules can be treated like 

 Nostoc. 



"Wasserbliithe."— 



Fig. 41. — Gloeotrichia: photomicrograph from a preparation gome of the CyaUO- 

 stained in cyanin and erythrosin; negative by Dr. W. J. G. Land. ^^^^^^^ ^^^^^ ^^ ^^^^^ 



on the surface of quiet or stagnant water. The name, Wasserbliithe, 

 "water flowers," was given because 

 the scums are often iridescent. Some 

 of the commonest forms are Coelo- 

 sphaerium and Anabaena (Fig. 42). 

 Some of the Chlorophyceae also oc- 

 cur as Wasserbliithe. Where the ma- 

 terial 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 



%» .n? 



A 



B 



Fig. 42. — Anabaena: A, hormogonium 

 showing well-defined nuclei; B, older filament 

 showing a spore and a heterocyst. 



