PHYCOMYCETES 



165 



The conidiophores appear singly. They are 

 much branched and near the apices of the 

 branches at maturity peculiar disk-like swellings 

 are prpduced, each of which originates circum- 

 ferentially about four tentacular tips inclined out- 

 ward so as to continue more or less the general 

 direction of the branch axis. Ovate conidia meas- 

 uring 16-22 x 15— 20 /x are produced singly, and 

 these germinate readily in water, emitting a germ 

 tube through an apically developed pore (Fig. 59). 

 Oospores are occasionally found. These are small, 

 26-35 /x. m diameter, light brown, and roughened. 

 In controlling this fungus general sanitary pre- 

 cautions must be taken and a maximum of light 

 and ventilation should be constantly afforded. 



Fig. 59. Germi- 

 nating Conid- 

 ium of Bremia 



XIX. THE LATE BLIGHT AND ROT OF THE POTATO 

 Phytophthora infestans (Mont.) De Bary 



Clinton, G. P. Downy Mildew, or Blight, Phytophthora infestans (Mont.) 

 De By., of Potatoes. Conn. (New Haven) Agl. Exp. Sta. Rept. (1904): 

 363-384. Ph.32-37. Ibid. (1905): 304-330. ph. 23-23. 



De Bary, A. Recherches sur le developpement de quelques champignons 

 parasites. Ann. d. Sci. Nat. Bot. 20 (4me Ser.): 1-148. ph. 1-13. 

 1876. 



De Bary, A. Researches into the Nature of the Potato Fungus — Phytoph- 

 thora infestans. Journ. Roy. Agl. Soc. 12 (2d ser.) : 240-269. Jigs. 

 1-8. 1876. 



Jones, L. R. Certain Potato Diseases and their Remedies. Vt. Agl. Exp. 

 Sta. Built. 72: 13-16. 

 (Short accounts also in several earlier bulletins and reports.) 



Jones, L. R. Disease Resistance of Potatoes. Bureau Plant Ind., U. S. Dept. 

 Agl. Built. 87 : 1-39. 1905. 



Stewart, F. C, Eustace, H. J., and Sirrine, F. A. Potato Spraying Experi- 

 ments in 1906. N. Y. Agl. Exp. Sta. Built. 279: 154-229. ph. 1-2. 

 Jigs. 1-4. 1906. (Cf., also, Bullts. 290, 307, and 311.) 



Stuart, Wm. Disease Resistance of Potatoes. Vt. Agl. Exp. Sta. Built. 122 : 

 107-136. 1906. 



Ward, H. Marshall. Diseases of Plants. The " Potato Disease," Chapt. 5 : 

 59-85. 1896. London. 



The late blight and rot of the potato is so generally known 

 that frequently this malady is simply called the " potato disease." 

 From an economic point of view it is the oldest potato malady, 



