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 



/ m 



Fig. 52. Saprolegniaceae. Water Mould, 

 sporangium before the discharge of spores. _. „„,.,^ „„„ „,^,„<i^cu ouuics uc.i.b >.... 

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

 clavatus, o— oogonium a— antheridium. 5. Apimnes Braunii, zoosporangium with germinat- 

 ing zoospores. 6. Aphanomyces ste-llatus: o— ooffonium and a— antheridium x 390, 7.-9. 

 Lj^^nZT't M "^^' ^,-, /°""^ ^oosporangium x 200. 8. Part of older zoosporangium with 

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

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



1-3. Saprolegnia Thureti x 200. 1. Zoo- 

 Same with biciliated spores being dis- 



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



6 



