OF THE PAEM AND GARDEN. 257 



become disorganized and rot. At this stage the out- 

 ward symptoms of the disease first become manifest, in a 

 sickly, yellowish appearance of the leaf and a reduced 

 growth of cane. As the roots continue to decay, these 

 symptoms become more acute, until by about the third 

 year the vine dies. Such is the course of the malady on 

 the European vine ( V. vinifera), when circumstances ai-e 

 favorable to the increase of the pest. When the vine is 

 about dying it is generally impossible to discover the 

 cause of the death, the lice, which had been so numerous 

 the first and second years of invasion, having left for 

 fresh pasturage. 



Mode of Spreading. — The gall-lice can only spread 

 by travelling, when newly hatched, from one vine to 

 another; and if this slow mode of progression were the 

 only one which the species is capable of, the disease 

 would be comparatively harmless. The root-lice, how- 

 ever, not only travel under ground along the interlock- 

 ing roots of adjacent vines, but crawl actively over the 

 surface of the ground, or wing their way from vine to 

 vine, and from vineyard to vineyard. Doubts have been 

 repeatedly expressed by European writers as to the power 

 of such a delicate and frail-winged fly to traverse the air 

 to any great distance. 



But there is abundant evidence as to their power of 

 flight; they have been caught in spider-webs in Europe, 

 and have been captured on sheets of pajier prepared witli 

 bird-lime, and suspended in an infested vineyard, and 

 there is no doubt that they can sustain flight for a cnn 

 siderable time under favorable conditions, and, witli tlie 

 assistance of the wind, they may be wafted to great dis- 

 tances. These winsred females are much more numerous 

 in the fall of the year tlian has been supposed. Whcre- 

 ever they settle, the few ezgs which each carries are suf- 

 ficient to perpetuate the species, and thus snreiid tlie dis- 

 ease, which, in the fullest sense, mav be called contagious. 



