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GRAPE DISEASE. 625 
vines which now flourish in this country are those which have 
fought the long battle in the past and have best resisted the enemy. 
They are, in short, best adapted to the circumstances, and by 
their more vigorous nature resist the hypertrophy of the bark 
caused by the punctures of the lice, and form new bark under 
it. The European v`nes, on the contrary, are not only of a more 
highly improved and tender character, but have not been accus- 
to! to the disease. They consequently succumb more readily, 
on the same principle that many diseases that are comparatively 
harmless among civilized nations, acquire greater virulency and 
play fearful havoc when introduced among savage or hitherto 
uncontaminated peoples. 
There may be other reasons such as the different modes of 
culture and differences of soil ; for in the French districts, so badly 
affected, the vines are either grown with a single stake or no stake 
at all, and their soil is generally much poorer than ours. In 
America, also, we know that there are several natural enemies of 
the louse, and these checks have, in all likelihood, never been 
imported into Europe with their prey. That the louse will in 
time find enemies and lose its acute power of doing harm even 
in Europe, is highly probable; and M. Planchon has already 
noticed that the infested vines in the latter invaded departments 
of Gard and Herault retained a comparatively greener color 
than in that of Vaucluse, first invaded. Such has been the 
history of the Hessian fly and a number of other insects im- 
ported into this country. These are the explanations I ven- 
ture, and whether they be generally accepted or not, the facts 
in. 
OUTWARD AND MORE VISIBLE Errects OF THE Root DisEASE.— 
As long as the lice are confined to the more fibrous roots which, 
in a measure, are renewed each year, the vines show no ecided 
outward signs of the malady, which may then be considered in its 
incipient stage. As they become multiplied and fasten on to the 
larger roots, their work becomes more visible in a sickly, yel- 
lowish appearance of the leaf; and a reduced growth of the vine 
is the result. As the roots waste away, these symptoms become 
more acute, and at this stage of the disease the lice have gene- 
_ Tally left, so that when the vine is about dying it is often difficult 
to find any trace of the cause of death. On the rotten roots 
little eight-legged mites are frequently met with, and they are 
AMER. NATURALIST, VOL. VI. 40 
