6 PLANT DISEASES 



In preparing a mushroom-bed, it is well known that the 

 spawn or mycelium rnust grow and spread in the soil for 

 some time before it yields a crop of mushrooms. The 

 spawn or mycelium is the vegetative part of the fungus, 

 doing the same kind of work done by the root and leaves 

 of a flowering plant, that is, obtaining and assimilating 

 food. The part popularly called a mushroom does not 

 represent the entire fungus plant, but is in reality only 

 the fruit of the fungus or sporocarp, its use being to produce 

 spores, the equivalents of seeds ; and it appears above the 

 surface of the soil so that the ripe spores may be scattered 

 by wind and rain, the mycelium or vegetative portion of the 

 fungus remaining underground. 



As a second example, take the black smut of oats. It is 

 well known that the only time this fungus can inoculate 

 and enter the tissues of the oat plant is just after the oat 

 seed has sprouted. At this period, if germinating smut 

 spores are present in the soil in which the young oat plant 

 is growing, their germ-tubes readily penetrate the delicate 

 tissues of the young oat, and once inside, the mycelium of 

 the fungus grows along with the oat plant until the latter is 

 nearly mature, when the fungus produces its powdery black 

 mass of spores in the fruit of the oat. To the popular mind 

 the appearance of the sooty mass of spores, being the first 

 outward and visible sign of the disease, is considered as 

 an early stage of its appearance, whereas the mycelium of 

 the fungus has been feeding on the substance of the oat 

 plant for months, in fact from the very earliest stage of 

 its existence. 



As a rule the vegetative part of a fungus remains out of 

 sight, penetrating the tissues of the matrix, or substance on 

 which it is growing, the fruiting portion or sporocarp of the 



