CHLOROPHYCEAE 



235 



C. orbicularis, and C. irregularis are equally common. C. scutata is 

 often found on the floating leaves of Polygonum amphibium. 



Chromo-acetic acid (1 g. chromic acid and 3 c.c. acetic acid to 100 

 c.c. water) is a good fixing agent. For finer details and for sections, add 

 6 c.c. of 1 per cent osmic acid. 



d..J 



Fig. 56. — Ocdogonium. A, oogonial, and B, antheridial filament of a dioecious species; n, 

 nucleus; p, pyrenoid; s, starch. D shows two groups of antheridia, with 16 antlieridia in the upper 

 group and 8 in the lower. Most of the antheridia contain two nearly mature sperms. C, Ocdo- 

 gonium nehraskense, a nanandrous species collected by Dr. Elda Walker; d, dwarf male. X300. 

 From Chamberlain's Elements of Plant Science (McGraw-Hill Book Co., New York). 



The epidermis of the host plants is hard to peel off. With a fleshy 

 plant, like Sagittaria, cut parallel to the surface pieces 8 or 10 mm. 

 wide, lay the outer side on a piece of glass, and gently scrape off the 

 hypodermal cells until practically nothing but the epidermis, with the 

 Coleochaete, is left. Then fix and mount the epidermis with the Coleo- 

 chaete. Stained in iron-alum haematoxylin and mounted whole, such 



