98 Minnesota Plant Diseases. 



The wind transports many fungus spores from plant to plant 

 and some great plant epidemics are due in part to this agency. 

 It seems possible that red rust spores may be blown from warm- 

 er climates, where they pass the winter, many miles, inocu- 

 lating in the early summer or spring the plants of northern 

 countries where the summer spores cannot be formed through- 

 out the year. Inoculation of some fungi occurs chiefly through 

 swimming spores and in such, only wet seasons will enable the 

 disease to become serious. Such a parasite as potato bhght will 

 spread with remarkable rapidity on plants in low, damp situa- 

 tions or during excessively moist weather. Some of the algal 

 fungi, as white rust, combine the two methods in distributing 

 by means of the wind, spores which in subsequent rainy weather 

 break up into swimming spores and thus act as new centers of 

 inoculation. Insects carry spores of fungi from plant to plant 

 and are allured by "honey dew" or by other sweet and odorous 

 liquids. In the case of ergot of rye the insects are attracted by 

 a honey-like fluid, which is exuded by the young grain, on 

 which the fungus has formed an abundance of summer spores. 

 These are then carried by the fly to other young flowers and the 

 disease thus spreads rapidly. It is known that many other ani- 

 mals effect the spread of plants by distributing spores under 

 favorable conditions. The furry coats of some rodents have 

 already been mentioned as depositories for spores. Man is re- 

 sponsible for many inoculations of fungus spores on plants. 

 All of the numerous methods of transportation and travel and 

 commercial intercourse furnish means by which man scatters 

 spores of fungi, often bringing them into most favorable condi- 

 tions. The introduction of mallow rust from South America 

 has already been cited. Careless pruning or wounding of trees, 

 untidiness in horticultural and agricultural pursuits and lack of 

 knowledge of the nature and various methods of infection of 

 certain diseases all conspire to make man an efficient aid in the 

 spread of fungus plant diseases. In manure heaps dangerous 

 fungi often multiply or pass the winter. The debris of trees or 

 other plants which have been diseased is also a menace. The 

 various farm implements, in passing from one place to another, 

 may carry spores and effectually scatter them. The sowing of 

 smut-infected oats without taking the precaution to kill off the 



