Division of Vegetable Pathology. 



JAMES ELLIS HUMPHREY. 

 Prof, of Vef/etuhle Physiology, State Agricultural Experiment Station. 



FUNGOUS DISEASES OF PLANTS. 



Various rusts., smuts, mildews, blights, and similar diseases of cul- 

 tivated plants have been generally known and dreaded since plants 

 began to be cultivated. Any understanding of the cause of these 

 troubles, of the conditions of their occurrence, and of their relations 

 to each other and to the plants they infest is a matter of compara- 

 tively recent acquisition even among botanists. Among American 

 farmers and gardeners, it is only recently that intelligent inquirv and 

 thought regarding these important sources of loss has been awakened, 

 and they are but just beginning to be popularly spoken of as fungous 

 diseases. With this increased popular interest has naturally arisen 

 an increased interest in their scientific investigation, which is as yet 

 but fairly begun, and in the practical application of our technical 

 knowledge in devising ways and means for checking the spread and 

 preventing the ravages of the pests. It is, doubtless, true that to 

 the average reader the term fungus carri'js with it no definite idea. 

 This is due partly to the newness of the popular use of the term and 

 the meagreness of generally accessible sources of information con- 

 cerning the fungi, and partly to the inherent difficulty and technical- 

 ity of the subject. To obtain a clear notion of organisms so small 

 as to be barely lecognizable by the naked eye and requiring high 

 powers of the microscope for their study, yet with such apparently 

 disproportionate capacities for mischief, is not easy. It is, for this 

 very reason, all the more important that, in a discussion of fungous 

 diseases intended for popular information, an attempt should be 

 made at the outset to remove, so far as may be, this i'undamental 

 difficulty. 



In the first place, then, a fungus is -a plant, as truly and essentially 

 a plant as the corn-stalk or rose-bush on which it grows. Yet it is 

 not only much smaller, but also much simpler than these. While the 

 plant-body of the corn or rose shows much specialization of structure, 

 having the various vegetative functions of the i)lant performed by 



