PLANTS AS DISEASE PRODUCERS 317 



the disease. Altogether, these epiphytotisms (epidemics) result either 

 when the conditions are favorable for the spread of the parasites, or 

 when the general tone and health of the plant has been lowered by 

 improper methods of handling, so that its disease-resisting capacity 

 has been reduced. Recognizing the possibility of the introduction of 

 other virulent fungous, or animal diseases, a stricter quarantine has 

 been instituted by both the individual state and national governments 

 with a careful inspection of nursery stock designed for shipment from 

 place to place. 



PROPHYLAXIS 



Prophylaxis may be defined as the means taken to prevent disease. 

 It includes a consideration of the methods of protecting plants from 

 disease, of preventing the spread of disease, and of the methods of 

 breeding by which the disease resistance of plants is increased until in 

 some cases absolute immunity is reached and the plant is made proof 

 against disease. Some diseases are preventible by the observance of 

 proper care in the cultivation of plants,^ and by habits of cleanliness, 

 when no refuse which might harbor insect or fungous disease is per- 

 mitted to remain, but is either destroyed, or rendered innocuous. 

 For example, vegetable and agricultural crops should be rotated, so 

 that the same crop would not follow upon the same piece of soil where 

 the animal or fungous parasite may be lurking. Neither should the 

 farmer attempt to cultivate certain crops in acid soils, or in low situa- 

 tions subject to frost action. Nor should seeds be placed in beds rife 

 with the spores of the damping-off fungus, Pythium de Baryamim. By 

 proper care on the part of the grower diseased plants should not be 

 sent away from an infected locality, and vice versa, he should be careful 

 about the introduction of nursery stock and plants from other localities 

 without a careful inspection. The national and state quarantine 

 regulations are designed to help the grower in these respects, and he can 

 refuse to purchase new plants without they are accompanied by a 

 certificate setting forth that these plants are free from animal and 

 fungous diseases. Orton- in two suggestive papers, has shown that 



^ BoLLEY, H. L. : Cereal Cropping: Sanitation, a New Basis for Crop Rotation, 

 Manuring Tillage and Seed Selection. Science, xxxvii: 249-250, Aug. 22, 1913. 



^ Orton, W. A.: International Phytopathology and Quarantine Regulation, 

 Phytopathology, 3: 143-151, June, 1913. The Biological Basis of International 

 Phytopathology, Phytopathology, 3: 325-333, February, 1914. 



