DISTRIBUTION OF PHYCOMYCETES 399 



Spongospora subterranea, causing powdery scab of potato, ap- 

 pears to be endemic to Equador and Peru. It has become estab- 

 lished throughout the British Isles, continental Europe, .Madagas- 

 car, the area bordering the Mediterranean Sea on the east and 

 south, South Africa, New Zealand, and Tasmania. The shipment 

 of infected tubers from one region to another undoubtedly is the 

 primary means of dispersal of this organism. 



DISTRIBUTION OF PHYCOMYCETES 



The lists of Bisby and his associates (1929) and of Bisby 

 (1933) indicate that 85% of all Phycomycetes present in Mani- 

 toba and 40% of those in India occur also in Europe. Of 35 

 species, mostly Mucorales, present in soil in North America 26 are 

 also European. The significance of nutrition as a factor in distri- 

 bution among Phycomycetes is apparent when the Peronosporales 

 are considered in contrast to other phycomycetous orders. The 

 distribution of Peronosporales, all obligate parasites, is definitely 

 limited by that of the hosts. 



Less is known regarding the distributional range of saprophytic 

 species of Phycomycetes in general than that of pathogenic spe- 

 cies, but Rhizopus nigricans and Mucor mucedo, both cosmopoli- 

 tan species, are notable exceptions. Seemingly both can thrive 

 wherever man lives, and both utilize the remains of numerous 

 kinds of plants as food. 



Students of soil fungi have shown that species of Mucor are 

 universally present in arable soils and also in many virgin soils. 

 Another soil-borne genus is Allomyces, which is peculiarly suited 

 to wet sites, its members being commonly regarded as "water 

 molds." Allomyces arbusciila, representative of this genus, has 

 been collected in wet soil on all continents. Since water molds 

 do not thrive in the oceans and since A. arbuscula is unable to 

 tolerate salinity, no explanation of its wide geographical range is 

 forthcoming. 



The distribution of coprophilous Phycomycetes, such as species 

 of Pilobolus, is conditioned, not by climate and soil, but only by 

 the migration of the herbivor. Browsing animals eat the sporangia 

 that are lodged on vegetation near dung piles. The spores germi- 

 nate when voided with the feces, and within a few days Pilobolus 

 will mature a crop of sporangia and discharge them. 



