THE GRAPE PHYLLOXERA IN CALIFORNIA. 17 
Too few American varieties, either nonresistant or resistant, are 
grown in the State of California at this time to have been con- 
sidered in this investigation. 
Intrinsic vigor of vines. — Vines of great intrinsic vigor always re- 
sist phylloxera attack better than naturally weak plants. 
Varieties of vines. — Amongst vinifera varieties grown in Cali- 
fornia, a few have shown certain resistance when inoculations have 
taken place several years after planting. Such are, in order, Flame, 
Tokay. Mission, and Muscat (Fresno district), and in a lesser degree 
Grenache, Chasselas, and Burger. Laboratory tests with certain 
varieties in which phylloxera lesions rotted rapidly have shown that 
Zinfandel, Thompson's Seedless, Carignan, Burger, and Muscat suc- 
cumbed more rapidly and Tokay and Grenache less rapidly. 
Destruction of a highly susceptible vine. — Under favorable con- 
ditions for rapid phylloxeration, the hypothetical progress of de- 
struction of a highly susceptible vine, as Zinfandel, with established 
roots may be set down as follows: During summer and fall a few 
larva? settle on a part of the root system; the following year in- 
festation spreads to the surface fibrous and fleshy roots, and to a 
certain extent to the large roots near the crown, and nodosities and 
tuberosities are formed. The third year the subterranean infesta- 
tion spreads pretty well throughout the root system, although it 
is rare to find year-old wood much attacked, for it appears that 
the habit of roots of this age to slough the outer layer of bark pre- 
vents the phylloxera? from retaining a hold, and compels those 
already settled to move to other more hospitable portions of the root 
system. In this year some of the larger roots decay under combina- 
tion of phylloxera attack and excessive moisture in the subsoil or 
become dried out from phylloxeration combined with too great 
drought, and thus the flow of sap between the feeding rootlets and 
the aerial portion of the vine is more or less cut off. This results 
in a shortening of cane growth and sometimes in an abnormally 
large crop of grapes. During this third summer as the larger roots 
die an emigration of young larvae takes place. Many winged forms 
also may be developed. The fourth year finds the larger roots in 
great part destroyed, the cane growth correspondingly reduced, and 
a large number of fibrous and fleshy rootlets sent out from the 
trunk just below the soil surface. The phylloxera? colonize these 
rootlets in spring, but leave them in summer, when they decay. There 
is also a heavy migration from the decaying roots farther down 
in the soil. In the autumn it is hard to find phylloxera on such a 
vine, and this explains the maxim that the best type of phylloxerated 
vine on which to look for the insect is not one badly stunted, but 
rather one with slight stunting of the canes; in fact, one in the 
1900°— 21 2 
