RHODOPHYCEAE 251 



Wash in a gentle stream of sea water for 24 hours. Stain in iron- 

 haematoxyhn, and then for 2-3 minutes in safranin (Fig. 63). This 

 short stain in safranin gives a faint rosy tinge to mucilaginous struc- 

 tures, but does not obscure the fine nuclear detail. In the nucleus of 

 the sperm, the chromosomes remain distinct, so that the number, 20, 

 can be counted from the time the sperm is formed (Fig. 63 C) up to 

 fertilization. 



With very delicate forms, like CalUthamnion and Griffithsia, the 

 washing may be in part or even wholly omitted, and the chromic acid 

 extracted by the lower alcohols, the material being kept in the dark. 



Corallina. — CoralUna and other forms whose surface is incrusted 

 with lime need special treatment. The following solution is good: 



Chromic acid 1 g- 



Glacial acetic acid 1 c.c. 



Sea water 100 c.c. 



Fix 24 hours, changing the fixing agent 2 or 3 times. Wash 24 hours 

 in sea water. 



If carefully applied, the following is a good method : Put the mate- 

 rial into 5 per cent glacial acetic acid (in sea water) and watch it. As 

 soon as the vigorous effervescence begins to subside, rinse in sea water 

 and transfer to Flemming's weaker solution, and fix 24 hours. Iron- 

 haematoxylin is best for figures, but for general structure the safranin, 

 gentian violet, orange combination gives beautiful results. 



