8 THE POPULAR SCIENCE MONTHLY. 



witness, by their leaves covered with abortive galls, to the futile 

 efforts the lice sometimes persist in making to build in uncongenial 

 places. 



Yet other elements come into play, and nothing strikes the ob- 

 server as more curious and puzzling than the transitory nature of these 

 galls, and the manner in Avhich they are found — now on one variety, 

 now on another. 



I was formerly inclined to believe that gallcecola was a necessary 

 phase in the annual cycle of the insect's mutations; in other words, 

 that it was essential to the continuance of the species, and was proba- 

 bly the product of the egg laid by the winged and impregnated 

 female. On this hypothesis I imagined that gallmcola was probably 

 the invariable precursor of radicicola in an uninfested vineyard, and 

 that, if galls were not allowed to develop in such a vinej^ard, it would 

 not suffer from root-lice. More extensive exj^erience has satisfied me 

 that the hypothesis is essentially erroneous, and that, while the first 

 galls may sometimes be produced by lice hatched from the fe^v eggs 

 deposited above-ground by the winged female, they are more often 

 formed by young lice hatched on the roots, and which, w^andering 

 away from tlieir earthy recesses, are fortunate enough to find suitable 

 leaf conditions. It is barely possible that under certain circum- 

 stances, as, for instance, on our wild-vines, where the soil around the 

 roots is hard and compact, gallcBCola may become more persistent, 

 and pass through all the phases belonging to the species without 

 descending to the roots — the eggs wintering on the ground, or the 

 young under the loose bark, or upon the canes. For a somewhat 

 similar state of things actually takes place with another plant-louse 

 {Eriosoma pyri^ Fitch), which in the Western United States normally 

 inhabits the roots of our apple-trees, and only exceptionally the 

 branches; while in the moister Atlantic States, and in England and 

 moister parts of Europe, where it w^as introduced from this country, 

 it normally infests the branches, and more exceptionally the roots. 

 But there are no facts yet known to prove such to be the case with the 

 Grape Phylloxera, even on our wild-vines, and I do not believe that it 

 ever is the case in our cultivated vineyards. 



As already indicated, the autumnal individuals of gallcecola descend 

 to the roots, and there hibernate. There is every reason to believe 

 also that, throughout the summer, some of the young lice hatched in 

 the galls are passing on to the roots ; as, considering their size, tbey 

 are great travelers, and show a strong predisposition to drop, their 

 natural lightness, as in the case of the young Cicada, and of other in- 

 sects which hatch above but live under ground, enabling them thus to 

 reach the earth with ease and safety. At all events, I know, from ex- 

 periment, that the young gallcecola, if confined to vines on which they 

 do not normally, and perhaps cannot, form galls, will, in the middle of 

 summer, make themselves perfectly at home on the roots. 



