MYXOMYCETES AND SCHIZOPHYTES 
169 
Good mounts may be made by the Venetian turpentine method. 
Species of medium size are more satisfactory for a study of the 
nucleus than the very large species. Fix in a chromo-acetic-osmic 
solution (1 g. chromic acid, 3 c.c. acetic acid, and 1 c.c. 1 per cent 
osmic acid). Stain in iron-alum haematoxylin, and follow the 
Venetian turpentine method. While the nuclei are easily seen in 
such preparations, still better views can be secured from sections of 
paraffin material fixed in the same solution or in Flemming’s weaker 
solution. The section should be about 3 p thick. After staining with 
haematoxylin, stain lightly with orange dissolved in clove oil. In 
paraffin sections the scattered condition of the material as it appears 
in thin sections is very annoying. As soon as the material is thor¬ 
oughly washed in water, arrange it so that the filaments will all have 
the same general direction. This will enable you to get longitudinal 
Fig. 32.— Oscillatoria: photomicrograph from a paraffin section 3 n in thickness and stained 
in iron-alum haematoxylin. X373. 
and 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 filaments 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 Figure 32. 
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. 33). Like all small filamentous algae, it may be 
dried on mica for herbarium purposes. Venetian turpentine mounts 
and paraffin sections are prepared as in Oscillatoria. Tolypothrix is 
even better than Oscillatoria for a study of the nucleus. 
Scytonema is a similar form which is fairly common. It is often 
found as a feltlike covering on wet rocks. 
