THE GRAPE PHYLLOXERA IN CALIFORNIA. 39 



attacked for years previous, it is unusual to find hibernants, except 

 at the base of large roots or on the trunk, because the roots that were 

 attacked the previous summer tend to rot badly when moistened by 

 winter rains, and consequently most of the hibernants remaining 

 thereon die, and only those higher up on sounder pieces of roots 

 survive in abundance. The basal part of a large root is not gener- 

 ally badly attacked during summer, and so there are not enough 

 tuberosities to rot it during the succeeding winter. 



A very noticeable tendency is for the hibernants to congregate in 

 masses. Such masses occur on the normal surface of the root, on 

 tuberosities, on nodosities, and under one or more layers of bark. 

 Perhaps in general on a grossly infested vine more masses occur 

 on the outside bark, but this is only because the preferred sheltered 

 places are too few and are inadequate to cover all the phylloxera?. 

 On younger vines a favorable location for hibernating is at the 

 foot of the stump. On older vines this position is not so generally 

 chosen. On vines which are only lightly infested the phylloxera? 

 often congregate at certain spots, while other spots, apparently as 

 favorable, are neglected. On the heavily infested vines all the favor- 

 able spots for hibernation are utilized, the majority of the insects 

 being forced to locate on the unsheltered outside bark of the root. 



In vineyards the growth and maturing of the hibernants in spring 

 extends over a period about as long as that covered by the entering 

 into hibernation in the fall. The growth first becomes apparent 

 about February 25, and proceeds until the time arrives when the 

 most tardy individuals mature. Immature hibernants are found as 

 late as May, but by April 15 the great majority have become mature. 

 Just as in the case of " entering hibernation," so in the " spring 

 development," a wide range occurs even on single given vines. The 

 earliest individual may commence growth two months or more 

 before the most tardy. On an average, it takes about five weeks 

 for the hibernants to mature after they have first shown perceptible 

 growth. On sound lesions this is shortened to as much as three 

 weeks, and on decaying portions of roots lengthened to as much as 

 eight weeks. Many of those on decayed roots die from ill nour- 

 ishment before maturing, but the majority of such move away to seek 

 better food. 



The forces which influence the growth of the phylloxera? in spring 

 are a reversal of those which impel hibernation in the fall. As 

 stated, the phylloxera? start to grow about the time when the sap 

 begins to flow. On dying vines in which the sap flow is either not 

 apparent or very weak, the phylloxera? on the more healthy roots 

 show perceptible growth in like manner to those living on healthy 

 vines, in which case their activity is supposedly due solely or chiefly 

 to meteorological effect. The spring growth on unhealthy roots 



