150 



Mycologia 



spore formation, in the above-mentioned zygomycetes, is extremely 

 fragmentary and certain of his figures suggest that his material 

 was poorly fixed. 



Methods 



The Saprolegnias were grown on small flies of the genus Droso- 

 phila. They were frequently parasitized by Olpidiopsis and Ro- 

 zella. Cultures on the flies were then transferred to slightly cooled 

 agar plates. A drop of water was then placed on each fly so that 

 the sporangiferous filaments might float out into their normal 

 position. Slightly cooled agar was then gently dropped over each 

 fly. The cultures were then exposed out-of-doors to quickly con- 

 geal the agar. The halo of filaments was still easily discernible. 

 Blocks of agar containing the entire host were now cut out and 

 transferred to weak Flemming and Merkel fixatives. The wash- 

 ing, dehydrating, and imbedding was done as usual. The sections 

 were cut 5 /x thick, stained with the Flemming triple combination, 

 cleared very quickly in clove oil, and mounted in Canada balsam. 



Cleavage in Saprolcgnia was also studied in hanging-drop cul- 

 tures, and Olpidiopsis was also studied in the same manner. The 

 Zygomycetes were cultured upon sterilized bread in jelly glasses. 

 In order to retain the loose, open structure of the bread, which 

 facilitates the growth of the mycelia, only a small amount of water 

 was poured into each jelly glass before sterilization. When the 

 sporangia assumed a snow-white appearance, under the hand-lens, 

 wefts of the fungus were cut out with sharp-pointed scissors and 

 immediately transferred to the fixatives. The conglomerated mass 

 of hyphae was then gently pushed down into the fixative and the 

 vial was shaken to dislodge the air-bubbles. The material was 

 fixed for 24-48 hours in Merkel's solution, or for one hour in one 

 part of weak Flemming and two parts of water, and then trans- 

 ferred to Merkel's fixative. By these means blackening of the 

 fungus was prevented and bleaching with hydrogen peroxide was 

 unnecessary. 



The fixative was now poured off and the vial was carefully 

 filled with water and tilted into a dish of water. The fungus was 

 repeatedly floated into a vial and transferred into fresh water. 

 The material, thus washed for two to two and one half hours, was 



