THE GRAPE PHYLLOXERA IN CALIFORNIA. 63 
For the first generation, eggs deposited by adult hibernants were 
secured from a Zinfandel vineyard, and thereafter only eggs de- 
posited in the cages and of known generations were used in the inocu- 
lations. 
The average growing periods of the summer generations of wing- 
less aphids varied from 34.5 to 18.25 days, but in all except two gen- 
erations this period ranged between 18.25 and 24.20 days. Individ- 
uals varied between 36 and 10 days. The winged forms developed 
more slowly than the wingless, nine individuals averaging 34^ days. 
The hibernants developed in an average of 6| months. 
Eggs were placed for the most part on roots never before infested, 
and tuberosities usually followed rapidly after the hatching of the 
larvae. Nodosities were formed upon side rootlets. The main roots 
were all between one-sixth and one-third of an inch in diameter. 
It was found that about 40 per cent of the larvae remained on the 
exposed portions of the roots, the rest finding their way to the other 
portions. In spring a large percentage and in summer and autumn 
a smaller percentage of larvae settled close beside the eggshells from 
which they had issued. In spring the larvae did not display a tend- 
ency to roam, but in summer and autumn they wandered consid- 
erably, especially if the root had begun to decay or was drying too 
rapidly. Similar conditions occur in vineyards, and it is in summer 
and autumn that the typical wandering larvae are found. 
Excluding the winged migrants and the hibernated individuals, 
the summary of the growing period of all the phylloxera? developing 
on living roots during the years 1913, 1914, and 1915 is recorded in 
Table XIV. 
Table XIV. — Summary of Table XIII. 
Number of individuals 114 
Average period of growth days 22.15 
Maximum period of growth do 36 
Minimum period of growth do 10 
Taking into consideration the individuals removed before they 
attained their full development, the average growing period is to be 
estimated at about 25 days. The cellar experiments with severed 
pieces of roots in 1911 and 1912 combined yielded an average of 
30.57 days, and the experiments in the cellar and incubator combined 
in 1913 averaged 34.16 days. The cellar temperatures of 1911 and 
1912 averaged about 1^° F. lower than the combined cage tem- 
peratures for the period 1913-1915 for the months from May to 
October, inclusive. The cellar temperatures for 1913 averaged about 
H° lower than the incubator temperatures for 1913 and about J° 
higher than the cage temperatures for that year. 
