TESTING GRAPE VARIETIES IN THE VINIFERA REGIONS. 13 
the resistance of the plant by favoring or hindering the dissemination 
or activity of the insect. For instance, climatic conditions affect the 
multiplication of the insect and it can travel hut little in sandy soils 
of a certain fineness. Then again, a variety which in one locality has 
splendid resistant qualities perishes in another locality having a 
similar soil but a different climate or in another locality having 
a similar climate but a different soil. 
This is due to the fact that some species are adapted to moist soils, 
while others are variously adapted to dry soils, deep soils, or shallow 
soils, and also to the fact that the root systems of different species 
vary in habit of growth, some assuming a horizontal and others a 
vertical position; some roots are thick and fleshy and others small 
and wiry; some are soft, while others are firm. (See PI. V.) Thus, a 
moisture-loving variety or one having a horizontal root system would 
not thrive in a dry, hot climate; neither would a variety with a deep 
root system thrive in a shallow, hard soil, or one adapted to a dry loca- 
tion thrive in a wet soil. For such reasons, a variety grown under 
congenial soil and climatic conditions will often prove more resistant 
than one of greater natural resistance grown under adverse soil and 
climatic conditions. 
Resistance to phylloxera is also influenced by the congeniality 
existing between vine varieties when grafted on other vine varieties. 
Causes like these, and there are many others, affect the resistant 
qualities of vines, and it is with the study of the adaptation of 
varieties to varying conditions and the congeniality existing between 
vine varieties that the researches reported in this bulletin are par- 
ticularly concerned. 
The European work in the selection and breeding of resistant 
stocks has been determined largely by the necessity that such stocks 
be adapted to calcareous-soil conditions rarely encountered in the 
present Vinifera regions of this country. This renders it necessary 
for us to undertake our own researches and determinations. The 
varying soil, climatic, and other conditions in California make the 
selecting of the right grape species in the reestablishing of vineyards 
on resistant stocks rather a complex matter. 
Of the 23 species of grapes native to North America, the 14 shown 
in Table III have been found sufficiently resistant to merit the 
attention of the viticulturist, and they are under test in the experi- 
ment vineyards of the United States Department of Agriculture. 
Table III shows their natural habitat, the locations, sites, and the 
character of soil they prefer, the habits of the vines, their relative 
season of leafing (Pis. VI and VII), their root systems (PI. V), the 
flowering and ripening of their fruit, the ease or difficulty of propagat- 
ing them, their suitability for either bench or field grafting, and their 
relative resistance to phylloxera, cold, dampness, heat, and drought. 
