56 BULLETIN" 903, IT. S. DEPARTMENT OF AGRICULTURE. 



been examined and its interior subjected for a few minutes to a tem- 

 perature several degrees in excess of that obtaining in the trench 

 immediately preceding the examination. 



Plate VII illustrates the details of the cages used for observing 

 the phylloxeras on living roots. By means of the pulley and stand 

 the cages were hauled up and set for examination. It is obvious that 

 only young vines could be used for this work, as 9-inch pots were the 

 largest used. The vines were planted in early spring, certain of the 

 longer roots, drawn through holes cut in the saucer supporting the 

 bottomless upper pot, being planted in the lower pots. Thus about 

 4 inches of root between upper and lower pots were available for 

 inoculation and observation. At the upper and lower ends of this 

 visible portion the root passed through glass cylinders, and the inter- 

 vening spaces between the root and cylinder were filled with sand 

 and cotton (sand only was used in the lower cylinders) to prevent 

 the escape of phylloxeras to the invisible portions of the roots, both 

 above and below. For the viniferas and nonresistant American 

 vines this, however, failed to answer the purpose in many cases. 

 Out of 22 upper pots, which were examined several months after 

 the exposed roots were inoculated and had suffered more or less 

 severe infestation, 18 developed infestation on their roots, show- 

 ing that phylloxeras had found their way up to the roots in the 

 upper pots. Out of 36 lower pots liable to infestation on their 

 roots by reason of the fact that the exposed portions of the roots 

 above were infested, the roots in 9 showed no infestation or indi- 

 cations of any previous infestation, whereas in 13 others infestation 

 occurred which had resulted from larvae successfully penetrating the 

 lower glass cylinders ; in the remaining 14 pots, infestation or signs of 

 previous infestation occurred resulting from wanderers reaching the 

 rootlets by penetrating cracks in the soil. In the case of the re- 

 sistants, the cylinders of sand and cotton packed between roots and 

 glass were effectual in preventing spread to the invisible portions 

 of the roots. On these vines the infestation was always very slight, 

 and the phylloxeras exhibited very little desire to travel. On a 

 Champini (rupestris X candicans), on which the phylloxeras in- 

 fested only the side rootlets, and which bore only a slight infesta- 

 tion, wandering larvas entered the soil and infested the rootlets of 

 one of the lower pots, but there was no penetration through the glass 

 cylinders. 



As temperature is a factor of importance in the development 

 of the phylloxera, the following comparisons (Table XII) of tem- 

 peratures are noteworthy, taken (1) inside the cages containing 

 living vines, (2) 2 feet below the soil surface, at a point in the 

 laboratory vineyard a few feet distant from the trench containing 

 the cages aforesaid, and (3) in the laboratory cellar: 



