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 phylloxerse 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 phylloxerse 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 phylloxeras 

 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 phylloxeras 

 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 phylloxeras 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 



