176 Methods in Plant Histology 



to show a pale, or even a brownish, color, due to the brownish walls 

 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 

 amount taken up by the water while standing in the water pipe being 

 detrimental. 



The species found in running water will usually conjugate within 

 a week when brought into the laboratory and placed in rain water or 

 tap water. Species belonging to quiet waters, when brought into 

 the laboratory and placed in a 0.2 per cent Knop's solution, are 

 likely to undergo rapid cell division and growth. After the alga 

 has remained in such a culture for a few days or for a week, conjuga- 

 tion may be induced by transferring to rain water or tap water, and 

 keeping the culture in bright sunlight. Conjugation may begin 

 within 3 or 4 days. Variations in temperature between 1 and 15 C. 

 have little influence upon conjugation. 



The following is a good fixing agent for most species of Spirogyra: 



Chromic acid 1 g. 



Glacial acetic acid 4 c.c. 



Water 400 c.c. 



Fix 24 hours and wash 24 hours in running water. Use the Vene- 

 tian turpentine method. With Magdala red and anilin blue the 

 most beautiful preparations are rather easily obtained, the spiral 

 chromatophore taking the blue and its pyrenoids the red. If the 

 material contains figures, stain in iron-haematoxylin. This will stain 

 the figures, but will hardly touch the chromatophore or cell wall, 

 thus allowing an unobstructed view of the figures. While figures 

 occur occasionally in the daytime, collect your material at night, 

 preferably near midnight. 



Spirogyra is easily imbedded and cut. 



