DISEASES OF CULTIVATED PLANTS 325 
these develop. The spores of fungi serve for them the same purpose 
as do the seeds in higher plants; by reason of the extreme smallness 
of the spores they are easily transported by the wind and become 
deposited like dust particles upon exposed surfaces. Certain resting 
spores survive on the fallen leaves or other parts and will be 
destroyed if these parts are burned. (See black-knot). The survival 
of organisms capable of infecting the new crop is certainly to be 
expected in plant diseases as in epidemic disorders among people. 
Some fungi which produce disease survive by their thread-like 
parts (mycedium) ina manner similar to the survival of Canada thistle 
quack-grass and the mints among troublesome weeds by their visible 
underground stems. A good illustration of this form of survival is 
found in the case of potato rosette; in this disease the masses of 
mycelium (sc/erotia) remain upon the surface of the potato tubers 
and unless destroyed by treatment of the seed will be ready for 
immediate attack upon the growing plants (sprouts), even before 
these have reached the outer air and taken on a green color. 
Similar survival may occur in cultivated soils, especially where 
the same or closely allied crops are grown in succession. ‘Thus the 
same fungus as that,of the potato disease first named, survives in 
greenhouse soils or in celery soils outdoors. 
RESTING FORMS AMONG FUNGI 
The active parasitic phases of fungi necessarily coincide with 
the activity of the host plants; it, therefore, follows in our temp- 
erate climates with alternating periods of activity and rest of 
growth and practical somnolence, that the parasites require to be 
mutually adapted to intermittent activity. Some spores will survive 
the brief rest period between harvest and seed time, as in a number 
of the various grain smuts and in grain anthracnoses. Here they are 
found simply adherent to the seed grain. 
Seed infesting parasites like the loose smut of wheat, the 
anthracnose of pea and bean, and a variety of other vigoraus species 
survive as resting mycelium, which remains virtually inactive so 
long as the parasitized seed is not exposed to conditions of moisture 
and temperature such as bring about germination. 
' /There are endless gradations between these instances of “rest- 
ing’? mycelium and the protected fruit cases of the higher type of 
fungi. Thus the perithecia or closed fruit bodies of the wheat scab 
fungus, develop shortly after harvest upon the infected glumes or 
culms of wheat, and may be observed by the unaided eye, as black 
bodies seated upon the pink mass of one summer form. ‘These fruit 
bodies in this case are the kind called ‘ ‘perithecia,’ which contain 
