224 



METHODS IN PLANT HISTOLOGY 



surface of the water. A few species occur in running water. The mats 

 are very sUppery to the touch — a character which assists in recogniz- 

 ing 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 of the zygospores. This 



C 



Fig. 48. — Zygnema: fixed in the Chicago chromo-acetic-osmic solution: A and B stained in 

 Magdala red and aniUn 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. 



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 amount taken 

 up by the water while standing in the water pipe being detrimental. 



