16 DISSEMINATION OF PARASITIC FUNGI 



confined to definite hosts, this would not be sufficient to account for so markedly 

 restricted a distribution if they were capable of wind dissemination for long 

 distances. 



From this consideration of the evidence available the conclusion to be 

 drawn is that in devising inetliods to ])revcnt tlio ii\trodnction of new diseases 

 of the type of those contained in the detailed list attached (which iiicludes a 

 considerable proportion of the destructive diseases introduced within the 70 or 

 80 years during which we have reliable records, and represents practically all 

 the classes of parasites likely to sjHead extensively in the future) infection by 

 spores carried through the air from, remote centres is not a contingency which 

 needs to be taken seriously into account. 



There remains the third method of the discontinuous spread of parasitic 

 diseases which depend on spores for their transmission — dissemination on 

 plants and other horticultural produce. The recognition of this as an 

 important means dates from a comparatively recent period and it is doubtful 

 if it is even yet fully realised. 



There is an abundance of evidence, both direct and indirect, that the spores 

 of most of the great groups of fungi are readily transmitted in a living condi- 

 tion, from one part of the world to another, on plants or parts of plants. 



All economic mycologists have probably had direct experience of the 

 transmission of living spores on plants or parts of plants ; many use it as a 

 means of exchanging material for study with more or less distant countries. 

 I have personally sent Indian parasitic fungi to workers in Europe, through the 

 post, with success on several occasions. The infective powers of the mildew 

 of wheat in India have been compared with that in England by means of living 

 ascospores, thus sent on withered wheat stems, and several of our Indian wilt 

 parasites of the genus Fusarium have been sent for purposes of study to Berlin 

 on the roots and base of the stem of their host plants. I have also found 

 living spores of two parasites of sugarcane on cuttings of American varieties 

 of cane received at Pusa from Louisiana, through the United States Depart- 

 ment of Agriculture, for trial in India. Quite recently I have received from 

 the same Department cultures on sterilised cotton stems of the American cotton 

 wilt Fusarium, and found the spores still living after the long journey to 

 India. Indeed cultures of fungi on nutrient material are now sent out all over 

 the world and there is a central bureau in Amsterdam for the supply of such 

 cultures ; a parasite on its host plant is very often in at least as favourable 

 circumstances for travelling as under these conditions. Presumably because 

 of its very familiarity few seem to have thought it worth while to record their 



