160 



Methods in Plant Histology 



Wasserbluthe. 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. 31). Some of the Chlorophyceae also occur as Wasserbluthe. 

 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 fil- 

 ter the water through 

 a cloth and finally 

 rinse the algae off into 

 a bottle. Enough 

 formalin may now be 

 added to the water in 

 the bottle to make a 

 3 per cent solution. 

 The material may be 

 kept here indefinitely, 

 but after a few hours 

 it is ready for use. If 

 the forms are small, 

 like Anabaena, smear 

 a slide lightly with 

 Mayer's albumen fixa- 

 tive, as if for paraffin 

 sections, add a drop 

 of the material and 

 allow it to dry over 



D and E, a heterocyst and a spore of A. gigantea drawn night Or for 24 flOUTS* 

 from paraffin sections stained in cyanin and erythrosin. . , 



then immerse the slide 



in strong alcohol for a few minutes, and then proceed with the 

 staining. Cyanin and erythrosin form a good combination for 

 differentiating the granules. Delafield's haematoxylin, used alone, 

 stains some granules purple and others red. Iron-alum haema- 

 toxylin is excellent for heterocysts. If the forms are large enough 

 to collapse with such treatment the Venetian turpentine method may 

 be employed. 



c 



D 



E 



FIG. 31. Wasserbluthe: A, Coelosphaerium Kiitzin- 

 gianum; B, Anabaena flos-aquae; C, Anabaena gigantea; 



