DISTRIBUTION OF SPORES 111 



vegetation for several weeks. Moreover the sporangial wall is 

 black, so that injurious radiations are screened out. 



There is no evidence that certain other coprophilous species, 

 for example, Lachnea stercorea and Humaria gramdata, have any 

 structural adaptations for such habitats. Undoubtedly many 

 species grow in dung quite by accident. At any rate, mycologists 

 have come to recognize that herbivorous animals are excellent 

 collectors of fungi. 



The human agency. lYian, unwittingly and wittingly in the 

 distribution of seed, seedlings, cuttings, nursery stock, bulbs, and 

 roots, has spread and will continue to spread fungi of economic 

 importance throughout the world. Many of these fungi have 

 caused him enormous financial losses. To relieve and prevent this 

 situation, both state and federal inspection services have been 

 instituted and quarantines established. 



In North America alien or exotic species appear to be much 

 more destructive than indigenous ones, as is evident from the 

 ravages of chestnut blight (Endothia parasitica), blister rust of 

 white pines (Cronarthnn ribicola), Dutch elm disease (Ceratosto- 

 mella idmi), late blight of potato (Phytophthora infestans), 

 downy mildew of tobacco (Feronospora tabacina), and willow- 

 scab (Fusicladhnn saliciperdum) . Furthermore, there is evidence 

 that pathogens introduced from one continent into another may 

 find conditions in the new land more favorable for development 

 in epidemic proportions, as did grape mildew (Plasviopara viti- 

 cola) and late blight of potato (Phytophthora infestans), intro- 

 duced into Europe from the New World, and coffee rust (Hemi- 

 leia vastatrix), introduced into Ceylon, presumably from Africa. 

 A list of rusts [Arthur (1929)] in Australia in 1906, comprising 

 161 species, is said to contain 30 species that are not indigenous. 

 Arthur also lists 41 species of rusts that have been introduced into 

 ^orth America, including such important ones as Cronarthnn 

 ribicola, Uromyces appendicidatus phase oli, U. appendicidatus 

 vignae, U. betae, U. caryophyUimis, U. trifolii, Puccini a arachidis, 

 P. asparagi, P. chrysanthemi, P. glumarum, P. graminis phlei pra- 

 tensis, P. graminis tritici, and P. mahaceamm. Undoubtedly man 

 distributes many fungi that cling to hands and clothing and are in- 

 oculated onto healthy plants inadvertently as he passes to them 

 after handling diseased plants. 



