Chlorophyceae 165 



sectioned, Flemming's weaker solution, or this solution with the osmic 

 acid still more reduced, is likely to give better results than chromo- 

 acetic mixtures without any osmic acid. A formula which gives 

 satisfactory results with Spirogyra may cause plasmolysis with 

 Cladophora. A few filaments should be placed under the microscope 

 in the fixing agent, and, if plasmolysis occurs, the chromic should be 

 weakened or the acetic strengthened until the suitable proportions 

 are determined. This is a slow process, but difficult forms like 

 Cladophora and Vaucheria are almost sure to shrink without it. 

 About 24 hours in any of the chromic series and a 24 hours' washing 

 in water will be sufficient for members of this group. Only a few 

 of the most commonly studied will be mentioned. 



With Marine Forms use sea-water in making up the fixing agents 

 and in washing, but use fresh water in making up alcohols and for the 

 10 per cent glycerin. 



Volvox. Volvox is found in ponds and ditches, and even in 

 shallow puddles. The most favorable place to look for it is in the 

 deeper ponds, lagoons, and ditches which receive an abundance of 

 rain water. Volvox is often associated with Lemna. It is not easy 

 to keep an abundance of Volvox in the laboratory. However, when 

 it disappears, do not throw the culture out, because new coenobia 

 are likely to develop from the oospores. 



For fixing, use chromo-acetic acid with 1 g. chromic acid and 

 2 c.c. acetic acid to 200 c.c. of water. The addition of 2 c.c. of 1 per 

 cent osmic acid to 50 c.c. of the solution named above will secure 

 more rapid killing and fixing and will bring better results if the 

 material is to be sectioned. 



The Venetian turpentine method should be used in making 

 mounts of the whole coenobium. A few broken bits of cover-glass 

 should be placed among the coenobia to prevent any pressure by 

 the cover. 



For paraffin sections, the material, preferably in sufficient 

 abundance to make a layer half an inch deep in the bottom of a bottle 

 as large as one's finger, is infiltrated with paraffin in the usual way. 

 In imbedding, simply pour the contents of the bottle out so as to 

 form a thin layer on a piece of glass. If a dish is used, the paraffin 



