THE INFLUENCE OF THE TANNIN CONTENT OF THE 
HOST PLANT ON ENDOTHIA PARASITICA 
AND RELATED SPECIES?’ 
MELVILLE THURSTON COOK AND Guy WEST WILSON 
The differences between species, genera, and families by which 
certain groups of plants are resistant to certain parasites while 
others are more or less susceptible are very generally recognized by 
all botanists. Actinomyces scabies attacks potatoes, turnips, beets, 
carrots, and parsnips, representing four different families. Pseu- 
domonas tumefaciens attacks a much larger range of host plants. 
Many familiar parasitic fungi and bacteria are restricted to certain 
families, to a few genera, or even to a single genus; others have 
similar restrictions as regards species; and still others are restricted 
to the races within the species. The same law will apply to the 
insects which cause the peculiar physiological or pathological 
structures known as galls. Cecidomyia pilulae occurs on a very 
large number of oaks, Amphibolips confluentus on four species, 
while the very common Andricus seminator occurs on but one. 
Individual plants which are more or less immune to destructive 
parasitic organisms have attracted the attention of the plant 
pathologists and plant breeders and have been the starting point 
for long series of selection experiments resulting in resistant varieties 
which are of great value to the practical agriculturists. Many 
theoretical explanations of the resistance or susceptibility of related 
varieties or species have been offered by botanists who should 
know better, but very few facts of real value have been collected. 
_ Marswatt-Warp’s studies indicated that the histological char- 
acters were of but little if any importance in aiding the plant to 
resist its parasitic enemies. He finally says: ‘Infection and resist- 
ance to infection depend on the power of the fungus protoplasm 
to overcome the resistance of the cells of the host by means of 
enzymes or toxins; and reciprocally, on that of the protoplasm of 
* A more complete discussion of the experiments given in this paper will appear 
in some of the publications of the New Jersey Agricultural Experiment Station, 
New Brunswick, New Jersey. 
Botanical Gazette, vol. 60] [346 
