50 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
Examination of Table VIII shows that the incubation period 
gradually becomes shorter as the temperature rises. 
The exposure to light apparently produced abnormal rapidity 
in the deyelopment of the eggs. In lot 18 this influence was scarcely 
felt, while in lots 1, -1, and 6 it was very cogent, and it is evident that 
exposure to light is chiefly influential under low 'temperatures. The 
comparatively slow development of lots 25 to 27 apparently can be 
laid only to temperature fluctuations obtaining in the incubator. 
This fluctuation in the incubator sometimes consisted in the mainte- 
nance of a lower minimum for a longer period than that which 
obtained in the main part of the cellar. Such temperatures possibly 
would exert a retarding effect upon egg development that would 
not appear in the averaged readings of the thermometer. 
Even among the lots kept in the cellar under similar conditions 
there were apparent exceptions to the rule that "the higher the 
temperature the shorter the period of incubation." One such instance 
is that of lots 15 and 16, in which two large series were used, yet 
under temperatures differing but 0.1° F. there was a difference in the 
average incubation periods of one and a half days. 
Among the individuals enumerated in Table VIII the maximum 
egg stage was 27 and the minimum 5 days. The respective average 
temperatures influencing the two individuals were dd° F. and 68° F., 
and both were incubated in the cellar. It was possible only to estimate 
an annual average incubation stage, and this was about 11 days. 
It should be added that eggs have been observed in December to 
incubate in a period exceeding 30 days, but it is unusual to find eggs 
at this time of year. 
Experiments conducted in the cellar demonstrated that eggs in- 
cubated as rapidly in arid as in humid surroundings, but submergence 
in water lengthened the incubation period, even imder equal tem- 
peratures. 
Incubation on living roots. — During the years 1913. 1914, and 
1915 biologic records were made on the living roots of young vines 
of viniferse and vinifera X American hybrids. A series of gen- 
erations were conducted during these three years, and incubation 
was observed for each generation. In most cases immediately after 
deposition the eggs were removed to an unifested root, but in some 
they were allowed to incubate where they had been deposited. The 
cages containing the experimental vines were all placed together in 
one trench, and the temperature was alike in all of them. Table 
IX indicates the incubation periods with reference to temperatures 
and time of year. The years are not given, as in some instances 
