18 DISEASES OF CULTIVATED PLANTS 



spread to most European wild plants belonging to the potato 

 family, and also to some cultivated representatives of the 

 family, as tomatoes, etc. 



The history of the introduction and spread of alien 

 fungi has yet to be written, but the examples given, with 

 others that could be enumerated, afford absolute proof that 

 such a condition of things does in reality exist, and probably 

 to a considerable extent. 



My own opinion is that when a plant is attacked by the 

 same fungus in a distant country, as that from which it suffers 

 at home, the fungus was in some way conveyed with the seed 

 of the plant. This refers to those plants that can be intro- 

 duced by means of seed, as cereals ; leguminous plants, as 

 beans, peas, lucerne, clover, etc. ; mangold, beet, and many 

 other plants. In the case of ' bunt ' ( Ustilago] attacking 

 cereals, we have absolute proof that spores are carried along 

 with the ' seed' ; why should a similar method of conveyance 

 be denied in other instances? 



At Nairobi, in British East Africa, climatic conditions are 

 favourable for the cultivation of many economic plants grown 

 in this country. Wheat, broad beans, and French beans 

 were sown, and for a time promised well, but eventually one 

 and all were completely destroyed by a fungus epidemic. 

 On examination it was found that each kind of plant had 

 succumbed to the same species of fungus known to be 

 destructive to these plants at home. The wheat was destroyed 

 by rust (Pucdnia graminis] ; a small amount of ' bunt ' 

 (Tilletia caries) was also present. The broad beans were 

 covered with rust (Pucdnia f abac], and the pods of the French 

 beans were distorted by the fungus called Colletotrichum 

 lindemuthianum. Now, is it more reasonable to assume, in 

 the absence of positive proof, that these kinds of fungi were 

 already growing on indigenous plants at Nairobi, than to 

 assume that spores were carried from England along with the 

 seed ? I think not. All varieties of beet and mangold originated 

 from the wild beet. Now wild beet is attacked by a rust called 

 Uromyces betae, and this fungus passed on to the cultivated 

 varieties, and has followed them to South Africa, Australia, 

 New Zealand, United States, etc. The wild beet is absent 

 from each of these countries, and beet rust only occurs on 

 beet, hence if the fungus was not conveyed with the seed, how 

 did beet become infected in New Zealand and other distant 

 countries ? 



