46 
AGRICULTURE: L. R. JONES 
Gilman working at Wisconsin and later at the Missouri Botanical Garden 
found that there is a 'critical soil temperature,' about 17°C., for such inva- 
sion. Below this the plants are not parasitized, even in the sickest soils while 
for some 10° above this the attack becomes progressively more virulent. 
Correlated with this is the experience that at lower soil temperatures, e.g., 
in cool summers, there is little disease even with susceptible strains and in 
hot summers there is a certain amount of infection even with our most re- 
sistant strains. It is theoretically possible, therefore, that a strain which 
was resistant in a relatively cool climate might prove susceptible when trans- 
ferred to a warmer region. As a matter of field trial, however, these resistant 
Wisconsin cabbage strains have proved similarly resistant under trials extend- 
ing from New Jersey to Iowa. 
Regarding the fourth question we may speak with considerable confidence 
also. Our earlier work was confined, as previously suggested, to one cab- 
bage variety, the Hollander. Selections which have since been made from 
other varieties, both in connection with our own investigations and by others 
in Ohio, Iowa and Maryland, have given encouraging results. We may be 
reasonably confident, therefore, that a Fusarium-resistant strain of cabbage 
may be secured from any vigorous established variety. 
If we do not ask for too much in the way of practical application we may 
safely go farther in the generalization as to the occurrence of disease resist- 
ance in plants. Plants are always varying of course, and this includes varia- 
tions in those factors which make them more or less susceptible or resistant 
to the attacks of any parasite. Unquestionably constantly increasing recog- 
nition of this principle will be given by plant breeders and plant pathologists 
in seeking to control plant diseases. On the other hand, experience indicates 
that with parasites of certain kinds including the Fusariums, it is relatively 
easier in practice to secure disease-resistant strains of host plants than it is 
with many other parasites, for example the common wheat rust. 
1 For a more detailed consideration of these matters reference may be made to Wis. 
Agric. Exp. Sta. Res. Bid., 38, The Control of Cabbage Yellows through Disease Resistance, 
by L. R. Jones and J. C. Gilman, December, 1915. 
2 Tisdale did his work on inheritance as a graduate student under the direction of Dr. 
L. J. Cole in the department of experimental breeding, at the University of Wisconsin. 
His results along these two lines have been formulated for publication in the Journal of 
Agricultural Research. 
