THE GRAPE PHYLLOXERA IN CALIFORNIA. 123 



of that industry and, it is estimated, has in the course of some 60 

 years destroyed about 75,000 acres of grapes. 



In many instances the insect has been distributed through the 

 agency of infested rooted vines imported into an uninfested district 

 or vineyard. In other cases the insect has been carried on vineyard 

 material. In no instance has the distribution been as rapid as that 

 which took place in the vineyard districts of France. The modi- 

 fied life cycle in California, i. e., sterility of the winged form, 

 coupled with topographic barriers, consisting of mountain chains and 

 dividing valleys, is in very great part responsible for this. 



VINEYARD DESTRUCTION. 



There is great variation in the rapidity of the destruction of vines 

 and vineyards by phylloxera. 



Apart from some variation in the different grape varieties, soil 

 conditions must be considered as of great importance. In poorly 

 drained soils the vines succumb much more rapidly than in well- 

 drained land. Accumulation of moisture in the subsoil materially 

 assists in the decomposition of infested roots, whereas if the subsoil 

 is well drained, vines may flourish notwithstanding infestations ex- 

 tending over many years. Vines attacked when young and before 

 their root systems have become established will succumb more rapidly 

 than will those infested at a greater age. 



The first indication of phylloxera in a vineyard occurs in the form 

 of one or more stunted vines and a premature yellowing of the 

 foliage. In time, adjacent vines will show similar indications, and 

 those first infested are more noticeably stunted. Gradually more and 

 more of the surrounding vines are affected, and those in the center 

 become very much weakened or die outright. Thus are formed the 

 so-called " oil spots " or foci for the distribution of the disease, which 

 may be likened to the ever-increasing concentric circles of waves that 

 are formed when a stone is cast into placid water. 



Following the initial infestation of a vine under favorable condi- 

 tions for phylloxera, the insects multiply rapidly, and within two 

 or three years increase their range to involve the entire root system. 

 Those which settle on the growing rootlets form fleshy lesions or 

 swellings, which are termed nodosities. These swellings are gener- 

 ally somewhat curved, the insect inhabiting a depression of the inner 

 arc. In the great majority of instances the insect stops further apical 

 growth of the rootlet, and thus the rootlet ceases to supply nourish- 

 ment to the vine. Although the percentage of rootlets thus infested 

 is often large, a vine of vigor can easily send out more and continue 

 to draw its nourishment from the soil. Other phylloxera? settle on 

 the older roots and in most cases cause swellings termed tuberosities, 



