82 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
a layer of wet sand placed in the bottom of the jar was conducive 
to the production of migrants. "When moisture was applied peri- 
odically to filter papers, the production of migrants was greater 
the more frequent the applications. 
"What effect, if any, temperature has upon the production of 
migrants can not be shown except that they are produced during the 
hottest months of the year. Contrasting the hot summer of 1913 
with the cooler one of 1914, it was found that the production was 
about equal each year. 
Migrants are produced in greater numbers in soils which retain 
moisture than in those which dry out rapidly. Otherwise no further 
influence traceable to soil conditions has been noticed. Although the 
general behavior of phylloxera differs considerably in relation to 
different types of soil, as between these different types the production 
of migrants does not appear to change. 
In the season 1914, 12 vinifera vines were growing in cages. These 
were inoculated in the spring, and six of them later treated through- 
out the summer and autumn with fertilizers applied in liquid form 
periodically. These fertilizers — nitrogen, potash, phosphoric acid, 
and magnesium — were combined in a normal fertilizer and also 
used in combinations in which one element was in marked excess. 
The fertilized vines produced noticeably larger nymphal infestations. 
In 1915 other potted vines were treated likewise, except that all 
the fertilizer was mixed with the soil at the time of planting, and 
the vines were not inoculated until a month later. In this series the 
number of nymphs was no greater or less on the fertilized vines than 
on the unfertilized. 
Migrants formed part of radicicole generations 2 to 5. those of the 
third generation being the most abundant. It was never observed 
that any of the first generation (direct progeny of the hibernants) 
became winged. 
NYMPHICALS OR INTERMEDIATE FORMS. 
The insects of the nymphieal type are intermediate in form between 
the winged migrant and the wingless radicicole. In their adult 
stage they vary largely. Grassi (11) has figured and described sev- 
eral individuals which represent stages in the variation. His speci- 
mens varied from a type which differed only from the radicicole in 
the possession of two or three extra eye facets and in longer append- 
ages to one which superficially resembled a nymph in that it had well- 
developed compound eyes and noticeable wing pads. This last type, 
however, upon close examination, differed from the nymph as follows : 
(l)The antenna? (fig. 8: compare with fig. 9, antenna of nymph) 
frequently bore two sensoria, as in the winged insect, but the basal 
sensorium was less developed than in that form: (2) the wing pads 
