THE GRAPE PHYLLOXERA IN CALIFORNIA. 41 
The spring growth began in the earliest individuals about Jan- 
uary 25; by the middle of March nearly all the phylloxera? were 
growing and about half were mature. Some individuals remained 
dormant as late as the middle of April, and the most tardy did not 
mature until the middle of May or even later. On very poor 
roots many never matured at all. The period of appreciable growth 
prior to the shedding of the first skin averaged two weeks and the 
period from first molt to maturity about three weeks. On vigorous 
roots the hibernants mostly developed without changing their posi- 
tions, but they forsook in large numbers roots decayed or decaying. 
These emigrations occur both before and after molting but chiefly 
just following a molt. 
In comparing the hibernation on severed roots as observed under 
cellar conditions with that on living roots as observed in the vine- 
yards, in pots, and in special box cages, several points are to be noted. 
(1) The phylloxeras on the severed roots in the cellar entered hiber- 
nation in a more irregular manner than did those on the living vines. 
This condition appears due to the following causes : The severed roots 
were cut off from a normal flow of sap, the temperature fluctuations 
in the cellar were greater, and in the months of July, August, and 
September the temperature reached a lower daily minimum than 
in the vineyards; (2) the phylloxera? hibernating in the cellar ma- 
tured earlier in the spring than those on living vines out of doors by 
reason of the higher temperature obtaining in the cellar during 
January and February; (3) there was a greater mortality among the 
hibernants in the cellar, due to the fact that the severed roots often 
dried up or decayed before spring; (4) numbers of the phylloxera? 
occasionally hibernated after they had shown appreciable growth 
or even cast a skin. This phenomenon rarely has been observed 
on living roots. In other respects the behavior of the phylloxera? 
on severed roots did not differ from that on living roots. In excep- 
tional cases vigorous pieces of severed roots were observed to send 
out fleshy rootlets in early spring, indicating a modified sap flow, 
and on such roots the phylloxera? moved early and appeared to 
be influenced by this flow of sap. The comparatively high winter 
temperatures obtaining in the cellar undoubtedly produced this modi- 
fied sap flow, since it occurred much earlier than the corresponding 
flow in the vineyards. 
Hibernation on vinifera vines in cages, 1913-14. — The following 
observations were conducted upon the roots of living vines of differ- 
ent varieties growing in special cages (Pis. V-VII, p. 52). The vines 
were young and satisfactory specimens for the experiments. The 
exposed portions of the roots between the upper and lower pots were 
about 4 inches long, one- fourth inch in diameter, and from 10 to 14 
inches below the soil surface of the upper pot. Although both ends 
