12 DISSEMINATION OP PARASITIC FUNGI 



is the blister-rust of the Weymouth or white pine. This tree 

 is a native of the east of North America and was introduced 

 into Europe about 200 years ago. In Europe it was attacked 

 by a rust which inhabits the European stone pine [Pinus 

 Cemhra) but which was unknown in North America. This 

 rust was noticed in Europe at least 50 years ago. Recently a 

 very large trade in seedling pines sprung up between Europe 

 (especially Germany) and the United States, and since 1903 it 

 is calculated that some millions of diseased pines have reached 

 the United States from Hamburg and elsewhere. The blister- 

 rust was found in the United States for the first time on these 

 pines, and has been detected altogether in more than 230 

 places, in all but one on impor-ted plants. In Europe the 

 pines are infected by air-borne spores from currant and goose- 

 berry bushes (on which the fungus passes part of its life) and 

 if these spores could traverse the Atlantic in the air, the pine 

 forests of America would have been infected long since. 

 The coffee leaf disease has been found in east and central Africa on 

 wild and semi-wild species of Coffea. It occurs as far west in 

 the Congo as at least longitude 23°E,, but has not been seen on 

 the West Coast. The disease became known first in the 

 epidemic outbreak in Ceylon in 1868. Since that date it has 

 spread to every coffee-growing country in the East and far into 

 the Pacific ; the spread has been gradual and the latest 

 recorded attacks are in the New Hebrides and New Caledonia, 

 which latter colony was reached in 1911. Yet the great 

 coffee-growing areas in South and Central America and the 

 West Indies are free from it, as also apparently the planta- 

 tions in Australia and Hawaii. If, as is probable, the parasite 

 is a native of East Africa, the home of the chief coffee plant 

 of commerce {Coffea arabica), long-distance wind dissemination 

 would be expected to carry it to West Africa where it would 

 have found host plants on which it can grow, and thence to 

 the West Indies and America. Its spread throughout south 

 and eastern Asia and the Pacific is readily exj)lained by trade 

 movements and the introduction of East African and Ar-abian 

 coffee varieties into the British, French, Dutch, and Spanish 

 colonies. There is probably little such movement across Africa 

 from east to west and the escape of the New World may be 



