207 
as used in a less restricted sense to include all types of over- 
owth. 
Metaplastic diseases.—See p. 8. 
Necrosis.—That type of pathological condition expressed by the rapid 
destruction of cell-structures and a consequent prompt death of 
the protoplasts; rots, blights and cankers are examples. 
Necrotic diseases.—See p. 7. 
Pathogene.—Any factor capable of initiating disease (usually a living 
organism). 
Pathogenesis.—That portion or phase of a life-cycle during which the 
pathogene becomes and continues directly associated with the living 
host. Pathogenesis includes inoculation, incubation and infection. 
Pathogenicity.—The ability of an organism to produce disease. 
Pathogenicity studies.—Experimental studies demonstrating the patho- 
genicity of a given organism. 
Pathological anatomy.—That phase of phytopathology which deals with 
pathologic changes in form, appearance, arrangement and relation 
of tissues in plant-organs (gross internal symptoms). 
Pathological histology.—That phase of phytopathology which deals with 
pathologic changes in the individual cells of plant-tissues. 
Pathological morphology.—That phase of phytopathology which deals 
with pathologic changes in form, size, color and the like, of plants or 
plant-organs (gross or external symptoms). 
Primary cycle.—A life-cycle initiated by a primary infection. 
Primary infections.—Those infections first initiated by the pathogene 
after a period of rest or relative inactivity. In temperate regions, 
pathogenes usually initiate their primary infections in spring or early 
summer. 
Protection.—The principle of controlling a plant disease by placing some 
protective barrier between the host and the generally-present patho- 
gene. Spraying, dusting and coating with substances inimical to 
the inoculum of the pathogene but harmless to the host are the usual 
protective measures employed. ; 
Range.—The geographical regions, areas or countries in which the disease 
is known to occur. ; 
Saprogenesis.—That phase of a life-cycle during which the pathogene 
is not in direct association with the living host. Saprogenesis 1n- 
cludes the saprophytic activities and dormant period of the patho- 
gene. Some pathogenes exhibit no true saprophytic activities 
during saprogenesis; some exhibit no saprogenesis, being continu- 
ously associated with the living host. : 
Secondary-cycle.—A life-cycle initiated by a secondary infection. 
Secondary infections.—Those initiated by inoculum from the primary 
or other secondary infections without an interposed resting or dormant 
period. : 
Syartome Tees pathologic changes by which a diseased plant is 
distinguished from a healthy one. For names and definitions of 
different kinds of symptoms, see pages 7-8. Soe ts 
Signs.—Incidental or experimental evidences of disease as distinguished 
from pathological evidences. For names and definitions of some of the 
more usual signs of disease in plants, see pages 8-9. ; 
Source of inoculum.—The place or object on or in which the inoculum 
is produced. 
