40 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



is curtailed and commences late. On nodosities and tuberosities 

 which have remained fresh during winter, the succulent condition of 

 the food induces early growth on the part of the phylloxera?. 



Hibernation under cellar conditions. — During the period 1911-1915 

 hibernation was observed on severed roots in the laboratory cellar. 

 These roots were kept in glass battery jars and in petri dishes and 

 remained in a fresh condition when systematically moistened. Good 

 callus growth and sometimes fleshy offshoots were obtained, es- 

 pecially when a layer of moist sand' was placed in the bottom of the 

 dishes. The phylloxera? caused the formation of lesions in similar 

 manner as on roots of living vines. 



Under cellar conditions hibernation was often prolonged beyond 

 the period found to occur in the vineyards, and this prolongation re- 

 sulted in a small number of phylloxeras maturing very late. The 

 " awakening " period in spring was not different from that found 

 in the vineyards under equalized temperatures. Under cellar con- 

 ditions a greater mortality existed among hibernants than in the 

 vineyards. This was supposedly due to the greater range of daily 

 temperatures, to the abnormal condition of the roots severed from 

 the vine, and to the apparent lack of sap flow. In the cellar hiber- 

 nants a greater variation in size and color existed, even in unmolted 

 phylloxera?, than in the vineyard on living vines. A very small per- 

 centage of hibernants were observed to pass the winter in the second 

 and third instars. Eggs were never observed to pass the winter, 

 since all eggs laid late in the year hatched in due course according to 

 temperatures. No mature or fourth-instar phylloxera? were observed 

 to hibernate. Adult radicicoles in late autumn, as at other times, 

 lived for some days or even weeks after they deposited their last egg, 

 but none was found that survived until spring. 



Observations on the hibernation of phylloxera? reared on sev- 

 ered roots under cellar conditions may be summed up as follows: 

 The first phylloxera? entered hibernation as early as August, in ex- 

 treme cases in July, and the percentage of hibernating individuals 

 from that time gradually increased. By October 1, it was found 

 that on the average about 30 per cent of the individuals were hiber- 

 nants. By the last of October from 85 to 90 per cent were hibernants. 

 All the living phylloxera?, however, were not hibernants until the end 

 of December, and during November and December a dwindling num- 

 ber of adults and unhatched eggs were observed. All larva? hatching 

 after November 1 settled down to hibernate, and about three-fourths 

 of those which hatched in October did likewise, the individuals com- 

 prising the other fourth maturing toward the end of October and 

 in November and continuing to deposit eggs up to December. 



