226 



METHODS IN PLANT HISTOLOGY 



Variations in temperature between 1° and 15° C. have little influence 

 upon conjugation. 



The Chicago chromo-acetic-osmic solution fixes well. Stain some 

 material in iron-alum haematoxylin and some in phloxine and an- 

 ilin blue. Use the Venetian turpentine method, and on each slide 

 mount material stained in both ways. With phloxine and anilin blue 

 the spiral chromatophore takes the blue and its pyrenoids the red. 



Fig. 50. — Scenedesmus 



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. 



Scenedesmus. — Scenedesmus (Fig. 50) is found everywhere as a con- 

 stituent of the fresh water plankton. It is more abundant in stagnant 

 water. It often appears in considerable quantity in laboratory cultures, 

 where it may be kept for years in a tightly closed glass jar without 

 renewing the water, the lid being removed only when material is needed. 



