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 
