LINNEAN SOCIETY OF LONDON. Iv 



comparatively harmless ; and a tuberculate form living in the 

 nodules it produces on the root-fibres, causing first the smaller and 

 then the main roots to rot, weakening, in the first instance, and finally 

 killing the whole vine. Each form has its winged generation. 



The insect is evidently of North-American origin, although the 

 precise history of its transmission to this country has not been 

 ascertained. It was first described by Asa Fitch, in the Trans- 

 actions of the New- York State Agricultural Society for 1854; but 

 living there chiefly on the leaves of the native vines, it had not 

 attracted any peculiar attention. More recently, however, Mr. Eiley 

 has found reason to attribute to the ravages of the subterranean 

 form the ill success of the various attempts made to establish in 

 America the European grape-vine. In England, where the intro- 

 duction of the insect from America may be readily conceived. Prof. 

 "Westwood's attention was first called to it in 1863, and again from 

 various quarters in 1867 and 1868, whence resulted the above- 

 mentioned account in the ' Gardeners' Chronicle ' for January 1869 

 (p. 109). "With us it does not appear to have much spread, and has 

 therefore not called for any further observation, the damp soil, 

 the mode of treatment, or other external circumstances proving un- 

 favourable for the development of the underground form. But 

 having by some means reached and established itself in the dry, 

 naturally-drained vineyards of the south of France, its general 

 character underwent a change ; natural selection at once gave an 

 enormous preponderance to the underground over the epiphyllous 

 form. It was first discovered there in July 1868 ; and by the close 

 of that year its ravages caused a panic among the vine-growers in 

 many parts of Lower Languedoc and Provence, similar to that which 

 we may remember in this country on the rapid spread of the potato- 

 disease in the autumn of 1845. It was immediately made the sub- 

 ject of scientific investigation, which has ever since been steadily 

 pursued. As one result Dr. Planchon inclines to believe that the 

 oidium and the potato-disease, like the Phylloxera, and, in former 

 days, the American blight of oiir apple-trees, had all been imported 

 from America. It would seem that all these parasites, whether 

 insects or fungi, capable of enormously rapid and extensive propa- 

 gation, remain unnoticed so long as they are kept in check by the 

 mutual relations of their constitution, habits, food, and other cir- 

 cumstances in which they are placed — but that the moment a 

 change, often very slight, in one or other of these conditions destroys 

 the balance, they may at once and suddenly gain the upper hand, so 



