Minnesota Plant Diseases. 91 



plants are artificially favored. The fertilizing of soils, the selec- 

 tion of various soils for certain plants, processes of cultivation, 

 and so on, are all directed toward this end. Men engaged in 

 these pursuits are fast learning to recognize the advantages and 

 profits of such processes and no improvement, however small it 

 may be, is too insignificant for notice and application. We 

 might term such processes improvements of health. 



There is another aspect which often escapes the busy prac- 

 tical farmer or horticulturist of today. In the absence of an 

 analysis he recognizes in disease only those sharply marked or 

 violent disturbances which are very obviously threatening the 

 life of his plants. The small losses by inconspicuous diseases 

 are often overlooked. For instance, no farmer fails to calculate 

 his loss when a heavy rust epidemic attacks his wheat or an 

 epidemic of smut invades his oats. Few farmers, however, 

 realize that every year rust levies a tax of a fraction of his crop, 

 although that fraction may be small. Why should he not be 

 alive to these facts and to the necessity for alleviating such 

 troubles as he is to the small improvements of cultivation and 

 introduction? And such conditions can only be improved by a 

 fair intelligence of the cause and spread of the diseases of plants. 



It is only by such knowledge that intelligent remedies are 

 applicable and the greatest profits attainable from the products 

 of the soil. It is only then that our plant proteges will at all 

 approach the highest mark of good health. 



It is a well known fact that the offspring of a plant may vary 

 considerably in their characters. If we take an extreme case 

 we can easily imagine two offspring of one plant to be so dif- 

 ferent in character that under the same conditions one would 

 thrive very well while the other would suffer very perceptibly. 

 The variation in the latter case would be indistinguishable from 

 disease for it tends under existing conditions to prematurely 

 end the life of that plant. Of course such a plant, if placed un- 

 der different conditions, might thrive exceptionally well, and 

 man's great interest in variation is the puzzle of fitting together 

 varieties and conditions to the best advantage. 



As seen in one light the life of a plant is unlimited in time 

 is, so far as we know, immortal through the germ cells which 

 contribute to the formation of new offspring. Individuals, 



