208 



MANUAL OF POISONOUS PLANTS 



In some forms the oospores are rare, and in the potato rot fungus they 

 have apparently not been found. In some members of this group oospores are 

 formed without fertilization, (Parthenogenesis). 



Dr. G. P. Clinton,* who has made a careful study of the Lima Bean Mil- 

 dew (Phytopthora Phaseoli) and the potato rot fungus (Ph. infestans) has 

 been unable to find that the mycelial thread of the antheridium had the same 

 origin as the one which bears the oogonium. It is possible that the fertiliza- 

 tion is accomplished in a manner similar to that given for some of the Mucors. 

 He says in a discussion of the potato rot fungus, "All of these facts are now in 

 favor, rather than against distinct mycelial strains (heterothallic forms) except 

 the last, which might indicate a homothallic form, one which contains both 

 antheridia on the same mycelium." 



SAPROLEGNIACEAE 



Hyphae, long branched, undivided; zoosporangia cylindrical oospores pro- 

 duced from sexual organs, terminal cells are cut off and converted into either 



Fig. 52. Saprolegniaceae. Water Mould. 1-3. Saprolegnia Thureti x 200. 1. Zoo- 

 sporangium before the discharge of spores. 2. Same with biciliated spores being dis- 

 charged. 3. The large spherical body, an oogonium and many oospores. 4. Dictyuchus 

 clavatits, o oogonium, o antheridium. 5. Aphancs Braunii, zoosporangium with germinat- 

 ing zoospores. 6. Aphanomyces stcllatits: o- oogriniuni and a antheridium x 390. 7. -9. 

 Leptomitus lacteus. 7. Young zoosporangium x 200. 8. Part of older zoosporangium with 

 zoospores (sp) and cellulose grains (c~) x 300. 9. Zoospores x 430. Fig. 1-3 after Thuret. 

 4-6 after DeBary. 7-9 after Pringsheim. 



* Rep. Con. Agrl. Exp. Sta. 1905: 304. 



