Journal of Applied Microscopy. 



507 



Fig. 9. Rivularia. 

 A. Nodule crushed under cover-glass. B. Four fila- 

 ments more highly magnified, showing heterocysts 

 at the base. 



to coagulate the albumen or immerse the slide in strong alcohol for a few 

 minutes, and then proceed with the staining. Cyanin and erythrosin is a good 

 combination for differentiating 

 the granules. Delafield's haema- 

 toxylin, used alone, stains some 

 granules purple and others red. 

 Iron alum haematoxylin is excel- 

 lent for heterocysts. If the forms 

 are large enough to collapse with 

 such treatment, the glycerine 

 method may be employed. 



If it is desirable to make 

 paraffin sections, put the mater- 

 ial, drop by drop, on a piece of 

 blotting paper until an appreci- 

 able layer of sediment is ob- 

 tained. Get the paper with its 

 material into paraffin by the usual 

 method, taking great care not to 

 wash the algae off. After imbed- 

 ding, trim away the paper and dip the block in melted paraffin. Sections can 

 now ,be cut and stained in the usual manner. 



Oscillaria. — For most purposes it is best to study Oscillaria in the living 

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

 stagnant water, on damp earth, and in other habitats. 

 The commonest forms have a deep blue-green or 

 brownish color. 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. For sections or 

 for glycerine mounts fix in chromo-acetic acid. 



Rivularia. — This form is readily found on the 

 under side of the leaves of water-lilies (Nuphar, 

 Nymphaea, etc.), but is also abundant on submerged 

 leaves and stems of other plants. It occurs in the 

 form of translucent, gelatinous nodules of various 

 sizes. Chromo-acetic acid gives beautiful prepara- 

 tions, but good results can also be secured from form- 

 alin or picric acid material. 



The most instructive preparations for morphological 

 study can be obtained by the glycerine method. Stain 

 in eosin or Mayer's haemalum. When ready for mount- 

 ing, crush a small nodule by pres-ing on the cover- 

 glass. Fig. 9 is drawn from such a preparation. The paraffin method is easily 

 applied, since the gelatinous matrix keeps the plants in place. Glceotrichia, 

 Nostoc, and forms of similar habit may be prepared in the same way. 



Fig. 10. Tolypothrix. 



b. A false branch. 



h. Heterocysts. 



