E, J. BUTLER 15 



plants are never exported, and in the absence of this means of 

 spread, the latter fungus has failed to reach other countries. It 

 has two spore forms, one suited admirably for wii\d dissemin- 

 ation but only capable of living for at most a few weeks ; the 

 other long-lived and resistant but only set free in the soil when 

 the diseased plants decor pose. 



Many other cases similar to these could be instanced, belonging to every 

 group of fuKgi and with every type of spore. It is difficult to believe that they 

 can all be due to deficient powers of acclimatisation, and many of them are 

 probably to be accounted for by the limited distances to which the spores can 

 be carried in the air in a living condition. 



Of the large groups of fungi whose geographical distribution opposes the 

 view that living spores can be borne for long distances in the air, the rusts afford 

 some intresting examples. In the genus Uromyces there are 119 species in 

 Europe, of which 70 are endemic (recorded up to 1911). Yet of the&e Europe 

 has only transmitted three {Uromyces Betce, U. caryophyllinus and U. Trifolii) 

 to North America, while two {Uromyces striatus and U. Fabce) are doubtful. 

 In turn it bas only received a single species (?7rom?/ces a/^^^^wt^^wZa/ws) from 

 North America, though the genus is very wsU represented there and no less 

 than 249 species have been recorded in North and South America combined, 

 of which 221 are endemic. It is worthy of note that all the exchanged species 

 are parasitic on cultivated plants. Australia, which has 32 species, of which 

 22 are endemic, has only received six fiom outside and these six arc the same 

 as those which have traversed the Atlantic, ^ Anotlier rust genus, Phrag- 

 midium, which is parasitic on plants of the N, 0. Rosacea, is also of interost 

 in its distribution. Over 60 species are known, but none are endemic in South 

 America (though there is one in the Falkland Islands) and only one has boon 

 introduced, Phragmidium disciflorum on roses.2 Though there are manv 

 species in southern and eastern Asia, only 4 (or perhaps only 2) are known in 

 Australia and only one of these has been introduced, the same one as to Soutli 

 America, also on roses. These rusts are not, so far as is knowT^, more exacting 

 than many other parasitic fungi in their climatic or other rgquircmcr.ts : their 

 spores are numerous and the least resistant type can often live for several weeks, 

 while the durable spores, that are set free as the host plant withers (or sooner 

 in Phragmidium), li\e for months ; and though they are strictly parasitic and 



1 The above details arc mostly on the authorit\' of P. Dictel {Ann. Mycol. IX, 1911, 

 p. 160) who has given special attention to the geographical distribution of rusts. McAlpine 

 (1906) gave a seventh species {Uromyces Polygoni) as having been introduced into Australia. 



9 Dietel, P. in Ann. Mycol, XII, 1914, p. 93. 



