DISEASES OF CULTIVATED PLANTS 339 
SOIL INFESTING PARASITES IN FIELD AND FORCING HOUSE 
The cultivated soil is a medium in which many species of 
bacteria and fungi survive from year to year. The public is famil- 
iar with the doctrine of bacterial infection or inoculation of the soil 
in its relation tothe nodules or tubercles of clover, alfalfa, soy beans, 
cowpeas and other cultivated plants of the Family of Leguminosae. 
One form of bacterium is not sufficient for both clover and alfalfa. 
This flora of the soil both in relation to bacteria and fungi of consid- 
erable range of species, is enriched by the applications of manure 
and by the practices of culture; by this is meant that the growing ofa 
given crop a second time ora third time consecutively in the soil 
increases the probability that the plant roots remaining in the soil 
are carried over from one crop to the next together with root 
parasites which cause dis- 
ease in the plants of this 
crop. Manifestly, like- 
wise, ifin preparation for 
a given crop to be grown 
for the first time upon the 
Jand, rather liberal appli- 
cations are made of fresh 
stable manure containing 
spores or mycelium, more 
especially the resting 
forms of mycelium called 
sclerotia, the soil will be- 
come infected by this 
manurial application. 
While this source of. in- 
fection is rather rare in 
field culture we bave spe- 
tific examples as in the ; 
isease of potatoe Fig. 19. Bases of potato stems (Carman No. 3) collected 
scab dise s a om oes June 7, 1902, Cheshire Ohio, showing injuries by Rhizoctonia, 
transmitted in this Way; The shaded areas are darker lesions occupied by an abund- 
ugar beets ence of Rhizoctonia hyphae; the tops showed conspicuous 
the scab of - & : in Rosette effects. Reduced from Bulletin No, 139. 
may be carried in like 
manner. But in forcinghouse culture where heavy applications of 
manure are made, the chances are greatly increased that soil infec- 
ion will be produced from the manure. 
It is of value to remember that seed infesting or seed infecting 
organisms are also very largely capable of survival in the soil nidus 
of cultivated soils, thus our troubles multiply adequately if our 
care be inadequate to avoid them. 
