VEGETABLE PATHOLOGY AN ECONOMIC SCIENCE 173 



incorporated with the soil in the spring may push it into a vigorous 

 growth the following summer, so that no trace of the symptoms can 

 be noticed. 



The study of root parasites gives us an additional reason for the 

 rotation of crops. In fact, judicious rotation of crops is one of the 

 best methods of shaking off and avoiding certain diseases. Nursery 

 stock of the peach, when grown in an old peach location where 

 a nursery or orchard has previously been located, will usually be seri- 

 ously affected with root troubles, such as crown-gall, root-rot, and 

 other fungus root parasites, eel worms or Heterodera, not to mention 

 root aphis and other insect troubles. This can be nearly all avoided 

 by growing the trees on a clean piece of land which has never been 

 in peaches. 



The application of lime to the soil has proved very beneficial in 

 preventing the club-root of the cabbage and allied plants. 



It should be noticed in this connection that not all diseases are 

 preventable by high culture. Certain diseases on fruit-trees, such as 

 pear-blight and apple-scab, more readily attack vigorous, well-fed trees 

 than th x ey do those growing moderately. Brown rot of the peach 

 attacks trees with large heavy foliage on rich soil , or where an excess 

 of nitrogenous fertilizer has been used, more seriously than it does 

 less thrifty trees. It is necessary, therefore, for the cultivator to 

 understand his particular plant as to its requirements and as to its 

 diseases. No one has to know plants so intimately as the pathologist. 



The early successes in the treatment of plant diseases have led to 

 vigorous prosecution of this work by the Government. The section 

 of Vegetable Pathology, of the Department of Agriculture, was or- 

 ganized in 1886, by one investigator. In 1888 there were four work- 

 ing pathologists. In 1893 there were nine. During the present season 

 there are about one hundred investigators employed in the Vegetable 

 Pathological and Physiological Investigations of the Department, 

 the majority of whom are now in the field studying the diseases of 

 plants. Considerable progress has been made by other governments, 

 notably France and Germany. Nearly every prominent experiment 

 station in the world has a plant pathologist on its staff. Our own 

 state experiment stations have at work in nearly every state in the 

 Union from one to five investigators. In Australia, in the Philippines, 

 in Java, in Japan, and, in fact, in nearly every country where scientific 

 botany is being pursued, contributions to the knowledge of plant 

 diseases are being made. 



