HOW FUNGUS DISEASES ARE DISSEMINATED 19 



Numerous other instances could be given of economic 

 plants that have been introduced to distant countries falling 

 victims to the same fungus disease from which they suffer at 

 home ; in fact this is true of every plant widely cultivated, and 

 I think proves my contention that the germs of the disease 

 are conveyed along with the seed in those instances where 

 seed is the only means by which a plant can be introduced 

 into a new country. 



In those cases where living plants, as fruit-trees, are sent to 

 distant parts, there is the double risk of introducing disease. 

 The fungus may be actually growing on the plant, or spores 

 may be nestling in tiny crevices or cracks in the bark or 

 adhering to the roots. Most destructive diseases, however, 

 attack the foliage and fruit, as ' apple scab ' (Fusicladium 

 dendriticum] ; ' brown rot ' (Monilia fructigena) ; ' bitter rot ' 

 (Gloeosporium fructigenuni] ; 'shot-hole' fungus (Cercospora 

 circumscissa}, etc. ; but as trees are exported during the 

 resting condition, when leaves and fruit are absent, these 

 diseases could only be conveyed under the form of spores. 

 It is quite possible, however, that the spores of many parasites 

 may be introduced along with ripe fruit in a living condition, 

 and, opportunity offering, establish a disease in a new district. 

 Other parasites, as apple-tree 'canker' (Nectria ditissimd], 

 grow on the trunk or branches, and could thus readily be 

 carried from place to place. 



The importation of rusted straw into a country is always 

 a source of danger to cereal crops. It has been proved that 

 even uredospores or summer spores retain their vitality much 

 longer than was at one time imagined. It only requires that 

 such rusted straw should be placed in the vicinity of a growing 

 crop, and the possibility or even probability of infection is 

 great. 



Certain kinds of minute fungi, Ascobolus, Pilobolus, etc., 

 that only grow on the dung of herbivorous animals, have 

 followed colonists to every part of the world. 



These fungi eject their spores to a considerable distance, 

 'some of which alight on living grass growing in the vicinity of 

 the dung on which the fungus is growing. When the spores 

 alight on grass, they are fixed by a kind of mucilage which 

 hardens when exposed to the air, and is not soluble in water. 

 If grass bearing these spores is eaten by some animal, the 

 spores commence germinating in the alimentary canal, and 

 soon produce a new crop of fungi on the dung. When hay 



