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Hypoplasia.—That type of pathological condition expressed by the failure 
of plant-cells or organs to complete, in one or more respects, their 
normal development, that is, arrested development. Dwarfing, 
failure of chlorophyl-development and the like, are examples. 
Hypoplastic diseases.—See p. 8. . 
Immunization.—The principle of preventing losses from a plant disease 
by the development of resistant or immune strains of the crop. This 
may be accomplished by selection and propagation of naturally 
resistant or immune individuals, by segregation and propagation 
of resistant or immune individuals obtained by crossing immune 
and susceptible forms or, artificially by feeding or injecting into 
susceptible hosts, substances which will make them resistant or 
immune. The last has, as yet, little or no practical value. 
Incubation.—The activities and developments of the pathogene from the 
moment of its arrival in the infection-court until it has established a 
pathologic relation with the host. 
Incubation period.—The period beginning with the arrival of the inoculum 
in the infection-court and ending with the first evidence of disease. 
Infect.—To initiate or produce disease. 
Infection.—The act of producing or initiating a diseased condition in the 
tissues of the host. Infection is progressive, developing cell by cell 
and continues as long as the host continues to react to the stimulus 
of the pathogene. 
Infection-court.—The place on or in the host where the incubation- 
activities of the pathogene take place; the immediate neighborhood 
of a possible point of infection. 
Infection period.—Commonly used to designate the period during which 
conditions (of host, pathogene, and environment) are especially 
favorable to inoculation, incubation, and initial infection, or to incuba- 
tion and initial infection only. 
Inoculate.—To transfer the inoculum from its source to the infection- 
court. 
Inoculation.—The act of inoculating. It includes all the phenomena in- 
volved in the transfer of the inoculum from its source to the infection- 
court. 
Inoculum.—That structure of the pathogene which may be transferred 
from its source to the infection-court. It usually consists of spores, 
seeds, eggs, thalli (of bacteria), or even mycelial fragments or pieces 
of stems (Cuscuta). 
Lesion.—A definite region in a plant or in one of its organs, characterized 
by a pathologic change in structure. 
Life-cycle-—The succession of phenomena exhibited during a period of 
continuous growth and development of the pathogene (in a fungus, 
from spore-germination to the normal death of the mycelium thus 
initiated). Most pathogenes exhibit in their life-cycles two rather 
distinct phases, pathogenesis and saprogenesis, 
Life-history.—The complete succession of phenomena characterizing a 
pathogene throughout the various cycles of its existence. 
Metaplasia.—That type of pathological condition expressed by the 
overgrowth in cells, other than increase in size (hypertrophy) or 
numbers (hyperplasia). Abnormal starch accumulation, abnormal 
development of. chlorophyl, unusual thickening of cell-walls and 
abnormal nuclear division or growth are evidences of metaplasia. 
