CHLOROPHYCEAE 
185 
covering the surface of the water. A few species occur in running 
water. The mats are very slippery to the touch—a character which 
assists in recognizing the genus in the field. In the larger species 
the characteristic spiral chromatophores can be seen with a good 
pocket lens, thus completing the identification, as far as the genus is 
concerned. Mats in which zygospores have been formed are likely 
to show a pale, or even a brownish, color, due to the brownish walls 
Fig. 39. — Zygnema: fixed in the special chromo-acetic-osmic solution: A and B stained in 
Magdala red and anilin blue; C and D stained in iron-alum haematoxylin. All show the nuclei, 
the chromatophores differentiated from the cytoplasm, and the large starch grains arranged radially 
about the pyrenoids. In C, cell division has just taken place and the pyrenoids and chromatophore 
in each new cell are dividing. In D, a young zygospore, the two nuclei have not yet fused. X790. 
of the zygospores. This color, however, is not always, or even 
usually, due to zygospores, but is more often due to the death and 
degeneration of the plants. Mats in early stages of conjugation and 
those with young zygospores show as bright a green as vigorously 
growing material. 
Spirogyra is not easy to keep in the laboratory. The small 
species keep better than the larger ones. Put only a small amount of 
the material in a jar and use rain water. If it is necessary to use tap 
water, let the water run for a minute before taking the water for the 
culture. Most metals are poisonous to Spirogyra, even the small 
