MYXOMYCETES AND SCHIZOPHYTES 



207 



Fig. 40. — Scytonema: filament showing 

 thick sheath and characteristic branching. 

 X640. 



anilin blue for the sheath, is good for Venetian turpentine mounts 

 (Fig. 40). 



Nostoc. — Nostoc is a cosmopoHtan form. It occurs on damp earth 

 or floating freely in water. In a fruit can or a battery jar, Nostoc is 

 easily kept year after year in the lab- 

 oratory. Young specimens are gener- 

 ally in the form of gelatinous nodules, 

 but in older specimens the form may 

 be quite various. It is very easy to 

 make sections, since the gelatinous ma- 

 trix cuts well and holds the filaments 

 together. Chromo-acetic acid is a good 

 fixing agent. Stains which stain the 

 gelatinous matrix make the prepara- 

 tions look untidy, but they show that 

 each filament of the nodule has its 

 own gelatinous sheath. Small nodules 

 may be stained in bulk and be got into Venetian turpentine. Crushed 

 under the cover, they make instructive preparations. 



Rivularia. — This form is readily found on the underside 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 preparations, but good results can also be secured 

 from formalin or picric acid material. 



The most instructive preparations for morphological study can be 

 obtained by the Venetian turpentine method. Stain in iron-haema- 

 toxylin and very lightly in erythrosin, the latter stain being used 

 merely to outhne the sheath. When ready for mounting, crush a 

 small nodule under a cover glass. The paraffin method is easily ap- 

 plied, since the gelatinous matrix keeps the filaments in place. Any 

 form of similar habit may be prepared in the same way. 



Gloeotrichia. — Gloeotrichia (Fig. 41), in its later stages, is a free- 

 floating form. In earlier stages it is attached to various submersed 

 aquatic plants. The nodules, when young, are firm like Nostoc, but as 

 they grow older and larger they become hollow and soft. The older 

 forms become so much dissociated that they lose their characteristic 

 form and merely make the fixing fluid look turbid. Allow a drop of 

 such material to spread out and dry upon a slide which has been 



