OE THE FARM AND GARDEI^. 



257 



become disorganized and rot. At this stage the out- 

 ward symjitoms 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 yine dies. Such is the course of the malady on 

 the European vine ( V. vinifera), when circumstances are 

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

 about dying it is generally impossible to discoyer the 

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

 the first and second years of invasion, haying left for 

 fresh pasturage. 



Mode of Spreadij^g. — The gall-lice can only spread 

 by trayelling, when newly hatched, from one yine to 

 another; and if this slow mode of progression were the 

 only one which the species is capable of, the disease 

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

 ever, not only trayel under ground along the interlock- 

 ing roots of adjacent yines, but crawl actiyely oyer the 

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

 yine, and from yineyard to yineyard. Doubts haye been 

 repeatedly expressed by European writers as to the power 

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

 to any great distance. 



But there is abundant eyidence as to their power of 

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

 and hav^e been captured on sheets of paper prepared with 

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

 there is no doubt that they can sustain flight for a con- 

 siderable time under fayorable conditions, and, with the 

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

 tances. These winged females are much more numerous 

 in the fall of the year than has been supposed. Where- 

 eyer they settle, the few eggs which each carries are suf- 

 ficient to perpetuate the species, and thus spread the dis- 

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



