THE GRAPE PHYLLOXERA IN CALIFORNIA. 
55 
of individuals lived from 90 to 105 days on a particularly innutri- 
tious piece of root without maturing. 
During 1913 two series of further experiments were undertaken. 
One series was reared in the cellar and the other in an electric in- 
cubator, the latter under somewhat higher temperatures. Genera- 
tions were followed from May to October. Table XI summarizes 
these observations. 
Tarle XI. — Development of radicicoles of the grape phylloxera, Walnut Creek, 
Calif., 1913. 
Environment. 
Genera- 
tion. 
Number 
of indi- 
viduals. 
Average 
period of 
growth. 
Average 
tempera- 
ture. 
Cellar 
Do... 
Incubator 
Do... 
Do... 
37. 25 
32.40 
35.60 
28.80 
29.70 
'F. 
65.1 
69.8 
65.6 
71.1 
70.3 
From this table it is noticeable that temperature exerted consider- 
able influence on the growing period of the aphids, and that warmth 
accelerated their development. In a series of generations reared in 
1915 on very nutritious food, recorded under the heading " Maximum 
and minimum generations yearly " (p. 71) , this temperature influence 
is very apparent. The greater constant warmth in the incubator in- 
duced the aphids to remain active later in the fall, after those in the 
cellar had hibernated. In comparing the 1913 series with those of 
1911, it was found that the aphids of the former developed more 
slowly than did those of the latter, and this notwithstanding the fact 
that both the series of 1913 enjoyed higher temperatures than did the 
cellar series of 1911. The roots supplied in 1913 were of much poorer 
quality than were those supplied in 1911. 
Development on living roots, 1913-1915. — During 1913, 1914, and 
1915 the habits and development of the radicicoles were observed on 
living roots of vines growing in cages (Pis. V; VI, fig. 1 ; VII) kept 
in a trench where the temperature approximated that obtaining 
beneath the surface of the Soil. As far as the temperature was con- 
cerned, the monthly averages ranged less than did those obtaining 
about 2 feet below the soil surface, but the daily fluctuations were 
considerably in excess of those in the soil. In the cages the roots were 
subjected to an average daily fluctuation of about 3° F. in summer 
and about 2° F. in winter. Two feet beneath the surface, the tempera- 
ture never fluctuated more than 1° in any given day. As far as could 
be observed, this temperature fluctuation had little effect on the 
growth of phylloxerse, except that it seemed to cause the nodosities to 
decay more rapidly than they would normally. Occasionally it was 
noted that some nodosities would dry up quickly after the cage had 
