136 BOARD OF AGRICULTURE. [Jan., 



from them, and appropriates to its own use the food materials 

 which arc found there. The fungus passes the winter in in- 

 fected seed potatoes. When such diseased potatoes are 

 planted the fungus grows up through the stalks and into the 

 leaves. Through the natural pores of the leaves it sends 

 branching threads which appear on the under side of the leaf in 

 patches of white mildew. These bear minute roundish cells 

 called by botanists " spores." The " spores " are functionally 

 the seed of the fungus, but being much more simple in struc- 

 ture* than the seeds of the higher orders of plant life, they are 

 designated as spores. The spores being very minute may be 

 carried in the air like dust, and are thus distributed to other 

 plants. Under favorable conditions of temperature and 

 moisture the contents of the spore divides into little bodies, 

 each of which eventually sends out a germ tube or filament. 

 This, if it happens to be on a potato leaf, penetrates into the 

 tissue of the leaf, and once having gained entrance to the 

 plant the fungus may spread even to the tubers. If it gains 

 entrance to the tubers it can be then kept through the winter. 

 There are many different methods of spore formation 

 found among the different classes of fungi. Many species 

 form summer spores which in function, though not in form, 

 are similar to those of the potato mildew. They vary very 

 greatly in size and shape, and in the way they are born on the 

 different fungi. These are produced under favorable growing 

 conditions, and serve for the immediate and rapid distribution 

 of the fungus. There may also be produced the mature form 

 of the fruit of the fungus in the shape of thick-walled spore 

 cases in which winter spores are finally developed. The 

 winter spores retain their vitality through periods unfavorable 

 to growth, and when conditions again become auspicious 

 they germinate, and start new centers of growth for the 

 fungus. Thus the mature form of the apple scab fungus 

 passes the winter in the fallen infested leaves of the apple. 

 When the leaves deca}^ in the spring these are spread, and 

 some of them lodge upon the apple foliage, and start the dis- 

 ease anew. The fungus of the black-rot of the vine passes the 

 winter in the dried diseased grape berries, and that of the 

 plum black-knot in the pustules, which develop in the plum 

 knots. The winter-form of the spores, which are produced 

 in these pustules, you cannot see with the naked eye on the 

 surface of the knot. 



