IMPLICATIONS 413 



fungus vegetation are bounded or delimited by climatic lines or 

 factors. These climatic factors operate by controlling the distri- 

 bution of the particular substrata, for both endemic and exotic 

 species. The provinces of fungi are delimited by such natural 

 barriers as climate, oceans, mountains, deserts, wind direction, and 

 vectors, but man has operated to break down these barriers and 

 to carry the fungi over them into new sites. 



Lind (1934) has also emphasized the influence of climate as a 

 factor in distribution. 



Of the 422 species collected in the Arctic, Lind indicates that 

 many occur also in the Alps and are otherwise widespread and 

 that no genus in these collections is endemic to the northern polar 

 region. 



Bisby's (1943) opinion is: "There are perhaps three times as 

 many [species of] phanerogams as fungi on earth." Moreover 

 saprophytic species generally have a wider distribution than do 

 parasitic ones, although distribution of substrata and hosts is of 

 primary importance as a control factor. 



The natural ranges and habitats of fungi tend toward the estab- 

 lishment of stability and biological balance. Man has always up- 

 set this stability by intensive cultivation of a given species of host 

 in a limited area, bv constructing artificial environments such as 

 cold frames and greenhouses, in which to grow plants, by attempts 

 to grow crops in new areas, and by introducing fungi into areas 

 where the environment unfortunately has too frequently proved 

 more favorable for the fungi than did their natural range. In re- 

 gard to the results of man's activities upon the distribution of 

 fungi, it is apparent that he has indeed made his own difficulties 

 and problems; nevertheless he seems to thrive in spite of his 

 tendency to learn things the hard way. 



There are good reasons for believing that some so-called new 

 diseases of cultivated plants are not caused by new species of fungi 

 but by old ones long present in a particular locality. As a result 

 of the conditions that obtain under cultivation, the host may 

 succumb to attack, whereas it might be immune in its natural or 

 native habitat. Of course, it must always be remembered that 

 both the susceptibility of the host and the aggressiveness of the 

 parasite are influenced by environmental factors which may 

 eventuate in a modification of the distributional range both of the 

 host and of the parasite. 



