ORDER PERONOSPORALES 



133 



Fig. 42. Peronosporales, Family Pythiaceae. Phijtophthora stellata Shanor. (A) 

 Habit sketch of hypiia with numerous sporangia and a sexual reproductive branch. 

 (B-E) Successive stages in the development of the same antherid and oogone, showing 

 possible explanation of the so-called amphigynous development. (F) Fertilization of 

 oogone. (Courtesy, Shanor: /. Elisha Mitchell Sci. Soc, 54(1):154-162.) 



Phytophthora infestans (Mont.) de Bary, the cause of the late bhght 

 of potato {Solarium tuberosum L.), tomato {Ly coper sicon esculentum Mill.), 

 and rot of potato tubers, was first observed as a serious enemy of the 

 potato about 1845. After being studied by various investigators it was 

 first fully described by de Bary in 1876. For many decades oogone forma- 

 tion was unknown in this species until Clinton in 1911 reported their 

 production in culture on oat agar. In 1927 Murphy reported finding them 

 on the surface of tubers and in the surrounding soil. As in some other 

 species these oospores were mostly parthenogenetic in origin although 

 a basal antherid was observed in one case. In P. phaseoli Thaxter, the 

 oogones were shown by Chnton (1906) to be produced in the seeds while 

 the conidiophores covered the surface of the pods of the lima bean (Phase- 

 olus Umensis Macf.). P. cactorum (L. & C.) Schrot. and some other species 

 are troublesome rot-producing and damping-off fungi of many kinds of 

 cultivated plants. 



The border line between some of the root-inhabiting species of Phy- 

 tophthora and some of the conidium-producing species of Pythium is so 



