Myxomycetes and Schizophytes 157 



remove the cover, allow the preparation to dry, and then return it 

 to the herbarium. 



Good mounts may be made, especially from the larger 

 species, by the Venetian turpentine method. Fix in chromo- 

 acetic acid and stain in iron-haematoxylin or in the Magdala- 

 red and anilin-blue combination. Either stain will show the nuclei 

 fairly well. 



For the best views of nuclei, thin sections are absolutely necessary. 

 Fix in Flemming's weaker solution, get the material into paraffin 

 by the gradual processes described in chap, ix; cut 2 to 5 ju in thick- 

 ness, according to the size of the species; stain in iron-haematoxylin, 

 and mount in balsam. In such mounts, the scattered condition of 

 the material as it appears in thin sections is very annoying. As soon 



FIG. 28. Oscillatoria: photomicrograph from a paraffin section 3/x in 

 thickness and stained in iron-alum haematoxylin. X373. 



as the material is thoroughly washed in water, arrange it so that the 

 filaments will all have the same general direction. This will enable 

 you to get longitudinal or transverse sections. As you begin with 

 the alcohols, use a Petri dish and lay a slide over the material, and 

 keep it there until you imbed in paraffin. This will keep the fila- 

 ments from spreading out too much, and you will be able to get as 

 much on one slide as you would be likely to get on a dozen slides 

 without such precaution. 



Oscillatoria, as it appears in section, is shown in Fig. 28. 



Tolypothrix. -This form occurs as small tufts, either floating 

 in stagnant water or attached to plants and stones. Some species 

 grow upon damp ground. It furnishes an excellent example of false 

 branching (Fig. 29). Like all small filamentous algae, it may be 

 dried on mica for herbarium purposes. Venetian turpentine mounts 



