DISTRIBUTION OF PHYCOMYCETES 401 



Bordeaux mixture as a fungicide. By 1907 the malady had reached 

 South Africa, and in 1917 it caused the first severe outbreak in the 

 vineyards of Australia. 



The tobacco downy mildew, Peronospora tabacina, endemic to 

 Australia, seemingly has been introduced both into North America 

 and South America, and there seems no reason for supposing it 

 will not spread eventuallv to other continents or countries. Evi- 

 dence indicates that it has been known in Australia for more than 

 50 years. It first appeared in Florida in 1921 and in Rio Grande 

 do Sul, Brazil, in 1938. Apparently it was eradicated from Florida 

 in the first season of its introduction, but it reappeared in 1931. 

 Since then it has gradually spread northward in the United States, 

 reaching Connecticut and Massachusetts in 1937 and southern 

 Ontario, Canada, in 1938. Clayton and Stevenson (1943) are of 

 the opinion, however, that this fungus is native to all temperate 

 regions having an indigenous Nicotiana flora. 



Influence of latitude. Meager data are available on latitude 

 as a factor in limiting the range of Phycomycetes, but it is ap- 

 parent that climatic zonation occurs. Phytophthora parasitica var. 

 nicotianae, for example, is regarded as tropical and subtropical 

 and was first recorded on tobacco from the East Indies in 1896. 

 Since then it has been found to occur on this crop in India, Japan, 

 Indo-China, the Philippine Islands, Nyasaland, Cameroons, 

 Uganda, Rhodesia, Puerto Rico, Jamaica, and Guatemala. More 

 recently the disease appeared in Florida, North Carolina, Virginia, 

 and Kentucky and in Greece, Rumania, and Bulgaria, all of which 

 are in the North Temperate Zone. In tropical regions tobacco 

 plants of all ages are subject to attack, whereas in more northerly 

 areas infection does not occur until the warmest weather, at which 

 season the plants are essentially mature. 



Choanephora cucurbitamm grows most abundantly in tropical 

 and subtropical regions but extends into adjacent temperate zones. 

 Collections of it have been reported throughout the East Indies, 

 Malaya, Burma, India, the Gold Coast, Sierra Leone, the West 

 Indies, and the southern United States, commonly on fading flow- 

 ers of cotton, okra, althea, squash, watermelon, cowpea, chili, 

 cassava, papaw, peanut, hibiscus, and dahlia. The closely related 

 Blakeslea trispora is quite restricted to tropical and subtropical 

 areas having abundant and frequent rains. During 1942, which 



