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234 BOTANICAL GAZETTE [april 



the adaptations recorded by Klebs (1899) In his detailed study 

 of Saprolegnia mixta. In this period a number of structural 

 peculiarities appeared, associated with the various sorts of nutri- 

 tion, and forms arose presenting the characters of three closely 

 related species, Saprolegnia mixta, S, monoica, and S. ferax. The 

 variation was most marked in respect to the presence, absence, 

 or relative quantity of antheridia which are the most important 

 distinguishing marks of these species. 



The original collection bore oogonia with relatively few 

 antheridia {^Saprolegriia mixta), and frequently none. By culti- 

 vating the form on a rich substratum — raw beef or fresh insects 

 — a much more extensive growth of antheridial filaments was 

 obtained, as in Saprolegnia ?no7ioica. On other media — boiled 

 -y whites and yolks of eggs and dried beef — the filaments never 

 produced antheridia, but oogonia were formed abundantly (as in 

 Saprolegnia ferax), normal in size and with numerous oospores. 

 After three months all cultures ceased to develop antheridia and 

 the number of oogonia steadily decreased until the cultures 

 reproduced entirely by zoospores. It was always possible to get 

 oospores, as Klebs (1899) has shown, by placing cultures devel- 

 oping zoosporangia under such conditions that the hyphae were 

 no longer submerged. This may readily be done by removing 

 material from water and placing it in a dish of cold agar-agar, 

 which will furnish enough moisture to support the fungus for 

 several weeks. The filaments out of water promptly developed 

 oogonia, even when they had the form characteristic of zoospor- 

 angia. Such cultures frequently showed club-shaped oogonia 

 whose eggs were arranged approximately in a line. 



Chromacetic acid proved to be the most satisfactory fixing 

 agent, but it must be employed much weaker than the usual 

 formula. One per cent, chromacetic acid caused immediate 

 contraction of the protoplasm, but a solution one-fourth per 

 cent, chromic and one-tenth per cent, acetic acid gave excellent 

 results, and presented advantages of clearness and preservation 

 over weak Flemming, Merkel, corrosive sublimate, sublimate 

 acetic, iridium chlorid, or picric acid. Paraffin sections were 

 cut 3-5/1 thick, and generally stained with safranin and gentian 



