CHLOROPHYCEAE 223 



istic chromatophores which are readily seen with a good pocket lens. 

 Sometimes conjugation can be induced by bringing the material into 

 the laboratory and placing it in open jars with plenty of water and not 

 too much hght. 



The chronio-acetic-osmic acid solution is good for fixing. Stain in 

 iron-alum haematoxylin and also in phloxine and anilin blue. Follow 

 the Venetian turpentine method, and in mounting put material from 

 both stains on each slide. Also, have both conjugating and vegetative 

 material on each slide. There will probably be vegetative filaments 

 mixed with those which are conjugating; but these will not be so 

 vigorous and are not so likely to show dividing cells and plastids as 

 material which has not begun to conjugate. Don't forget to run the 

 material up to 85 per cent alcohol and then run it back before staining. 

 To many, this may seem unnecessary, but the results are worth the 

 time and labor. 



Textbooks describe ''stellate chromatophores" in Zijgnema. A good 

 preparation should show that the chromatophores have an even out- 

 line, with no trace of a stellate form. The boundary between the 

 chromatophore and the protoplasm — often of a stellate form — in 

 which the chromatophore is imbedded, should be seen in well-fixed 

 material with either of the foregoing stains. The large starch grains, 

 extending from the pyrenoid almost to the border of the chromato- 

 phore, are better differentiated by the phloxine and anilin blue; the 

 nucleus and pyrenoid are better stained by the iron-alum haematoxy- 

 lin. Careful staining should bring out the features shown in Figure 48. 

 The chromatophores do not stain as readily as those of Spirogyra, and 

 consequently it is necessary to use stronger stains or more prolonged 

 periods. Use the Venetian turpentine method. 



For a detailed study, imbed in paraffin and cut thin sections. After 

 washing in water, arrange the filaments so that most of them will have 

 the same general direction; then, in running up through the alcohols, 

 keep the filaments from spreading too much by placing a slide on the 

 material. After imbedding, the material can be cut into blocks about 

 a centimeter square. If sections thinner than 5 fx are wanted, cut out 

 smaller paraffin blocks. 



Spirogyra. — Probably no alga has been more studied by pupils, 

 teachers, and investigators than Spirogyra (Fig. 49). Nearly all of the 

 numerous species belong to the low, quiet waters of ponds and ditches, 

 where they often form large, flocculent green mats nearly covering the 



