26 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



been observed wherein vines flourished with their vitality but 

 slightly impaired, notwithstanding a nodositous infestation extend- 

 ing over several years. One such instance was that of a 20-year-old 

 vineyard of Burger and Chasselas (viniferse) near Napa, Calif. 

 In 1913 the vines had been phylloxerated for upward of eight years, 

 and each year the nodosities had been extremely abundant and prac- 

 tically no tuberosities had been developed, yet the vines appeared 

 quite thrifty, owing to the maintenance of a sufficient number 

 of uninfected feeders. It is the decay of the tuberosities on the 

 larger roots, which the vine can not replace, that causes at first the 

 impairment of the vine's functions and later results in its death. 

 The simultaneous decay of many tuberosities is the cause of rapid 

 decline in the vigor of a vine and is the prelude to the vine's death. 

 The larger roots near the crown of the vine are especially susceptible 

 to tuberositous decay, while the decay of a root below the crown 

 is often very slow. This lower portion under favorable conditions 

 is able to maintain itself undecayed for months, if not years, and is 

 capable of providing nourishment for phylloxerse. It is frequently 

 observable that vines retain their vigor despite a ring of decay at 

 the crown of the roots, and do not become stunted until the major 

 portions of the larger roots have rotted. 



In a discussion of the effect of root lesions on the health of vines, 

 emphasis should be placed upon the decay of the tuberositous le- 

 sions and upon the fact that this decay is invariably hastened by 

 moisture and retarded by dryness. Decomposition is often hastened 

 by the work of fungi, molds, thysanurans, and tyroglyphid mites. 

 The most common mite so working is Rhizoglyphus elongatus Banks, 

 specimens of which were determined by Mr. Nathan Banks. It is 

 a rather large species and is very prevalent throughout the grape 

 sections of California. It was frequently reared on decaying roots 

 kept in the cellar of the laboratory. The mite is hyaline white, 

 with two brown circular spots, one behind the other, on the dorsum 

 of the abdomen. 



NOMENCLATURE AND SYNONYMY OF THE GRAPE PHYLLOXERA. 



The genus Phylloxera was erected in 1834 by Boyer de Fons- 

 colombe (10). The type species is P. quercus de Fonscolombe. In 

 1856 Asa Fitch (9) described the grape-leaf gall louse as Pemphigus 

 ■vitifoliae. The species was obviously placed in the wrong genus. 

 In 1867 Shimer (21) erected a new family (Dactylosphaeridae) and 

 a new genus, Dactylosphaera, for a new species of his (globosvm) and 

 tentatively placed vitifoliae Fitch in this new family and genus. In a 

 footnote he also proposed the genus Viteus for Fitch's insect. In 1868 

 Planchon (20) described the grape root louse from France as Rhyz- 



