46 SIXTH ANNUAL REPORT 



has been supposed by eiilomologists. Wherever they settle, the few 

 eggs which each carries are sufficient to perpetuate the species, and 

 thus spread the disease, which, in the fullest sense, may be called con- 

 tagious. Whether in a state of nature these winged females show a 

 preference for any one part of the vine in the consignment of their 

 eggs, is not yet known. It is quite certain, however, that they do not 

 reenter the ground. Neither do we know whether — in the light of 

 Balbiani's discoveries regarding the European Oak Phylloxera — the 

 young hatching from these eggs produce the diminutive sexual indi- 

 viduals already described. In confinement I have had such eggs 

 deposited both on the leaves and on the buds, and from the preference 

 which, in ovipositing, these aerial mothers showed for little balls of 

 cotton placed in the corners of their cages, I infer that the more 

 tomentose portions of the vine, such as the bud, or tiie base of it 

 leaf-stem, furnish the most appropriate and desirable nidi. On this 

 hypothesis it is quite possible for the insect to be introduced from 

 vineyard to vineyard, or from country to country, as well upon cut- 

 tings as upon roots. 



The young lice from the unimpregnated winged females hatch in 

 ten or twelve days after the laying of the eggs, under favorable con- 

 ditions of temperature. It is possible, however, that the later depos- 

 ited eggs remain unhatched throughout the winter. The few young, 

 from such eggs, which I have had, were neglected through absence 

 from home, and unfortunately (Balbiani's discovery was unknown to 

 me at that time) none were preserved. I can not say positively, there- 

 fore, that they were not mouthless and sexual, but a superficial exami- 

 nation revealed no characters which would distinguish them from the 

 young of the apterous females. 



Susceptibility of different Vines to tue Disease. — As a means 

 of coping with the Phylloxera disease, a knowledge of the relative 

 susceptibility of different varieties to the attacks and injuries of the 

 insect is of paramount importance. As is so frequently the case with 

 injurious insects, and as we have a notable instance in the common 

 Currant Aphis (Aphis rihesii), which badly affects the leaves of some 

 of the Currants, but never touches the Gooseberry which belongs 

 to the same genus, the Phylloxera shows a preference for and thrives 

 best on certain species, and even discriminates between varieties; or, 

 what amounts to the same thing, practically, some varieties resist its 

 attacks and enjoy a relative immunity from its injuries. It would, I 

 fear, be useless, and certainly unnecessary here, to attempt to ascer- 

 tain the reason why certain vines thus enjoy exemption while others 

 so readily succumb; but in a broad way it may be stated that there 

 is a relation between the susceptibility of the vine and the character 

 of its roots — the slow-growing, more tender-wooded and consequently 



