8 
Canker—the term applied to definitely delimited necrotic lesions 
in the bark of woody plants or the cortex of herbaceous stems; smooth 
or roughened, sunken or raised. 
HYPOPLASTIC DISEASES—those in which the most striking effect 
on the plant is a halting in some feature of its normal growth and develop- 
ment resulting in such symptoms as:— 
Dwarfing—the term applied in those cases where the plant or organ 
does not reach normal size. Special terms like, curly-dwarf, leaf-roll, 
spindling-sprouts, and little-peach, are but disease names used to designate 
peculiar forms of dwarfing. 3 : 
Chlorosis—used to designate the failure of or insufficient development 
of chlorophyl. Especially characteristic forms of chlorosis have been 
designated by such names as, mosaic, calico, frenching, and yellows. 
METAPLASTIC DISEASES—those in which the most striking effect 
of the disease is the overgrowth or overdevelopment of the affected tissues 
or organs. Stimulation of growth and development beyond the normal 
results in.such symptoms as:— : 
Hypertrophy—the term used in its broadest sense to designate all 
abnormal overgrowths in size of diseased parts or organs. Among the 
specially designated forms of hypertrophy are, galls, knots, and tubercles, 
which are more or less globose swellings of leaves, stems, fruits or roots 
resulting from the stimulating activities of such causal factors as insects, 
fungi, bacteria and mechanical injuries. Combinations with the names of 
the plant-organs affected give the terms, crown-gall, root-gall, root-knot, and 
root-tubercles. 
Witches’-brooms—broom-like growths resulting from the dense 
fasciculation or clustering of branches due to the forcing of adventitious 
buds from or about the diseased tissues. 
Hairy root—abnormal root development of the same character and 
nature as witches’-brooms on the limbs. 
Scab—definite areas on fruits, tubers and other organs usually 
due to injury followed by abnormal cork-development resulting in a rough 
raised or sunken spot. 
Curl—a term applied usually to overgrowths of leaves resulting in 
a thickening and fluting or puffing of the diseased areas, usually accom- 
panied by abnormal coloration. 
SIGNS 
The more striking and diagnostic signs of disease are the characteristic 
fruiting structures of the pathogene. Some of these have received patho- 
logic designations, as:— 
Smut—the black powdery spore-masses developed by the so-called 
smut-fungi. Found usually in the fruiting structures of the host, although 
sometimes in leaves and stems. 
Rust—the yellow, red, brown or black powdery spore-masses of the 
rust-fungi usually produced in small pustules on leaves and stems. 
Mildew—the superficial mycelial or conidial structures developed 
by certain fungi on the lesions. When such growths are mealy or silky 
they are designated powdery mildews, when fluffy, downy mildews. The 
former are usually white and on the upper surface of the leaves, while the 
latter are usually grey or purplish and on the under surface. 
