July 15,1924 
Depth Distribution of Root-Knot Nematode 
95 
in nematode content of the particular 
spots of ground where the samples were 
taken. For this series of experiments, 
these spots were unfortunately in 
widely different parts of the field, which 
naturally introduces an uncontrolled 
difference factor, even though the spots 
were chosen in each case on account of 
severe infestation in the crop preceding. 
abundant below the tenth inch, and 
were numerous to the maximum depth 
examined, 34 inches. In August they 
were numerous down to 18 inches, and 
were present in medium or less quanti¬ 
ties to the full depth. In September 
they were extremely abundant in the 
first 14 inches of soil depth. From De¬ 
cember to April the nemas appear to 
0 /-/00/M2W24 46 60/if 
Fig. 2— Depth distribution of root-knot nematodes in sandy loam soil at Brooksville, Fla., from June 28, 
1920, to May 28, 1921. The shading indicates the approximate number of knots that developed on 
tomato plants grown in the soil samples. The results are the average of four samples. The curve 
connects central points of regions of maximum infestation. Temperatures in degrees centigrade at 2 and 
12 inch depths are also given, these figures being the average for the week preceding date of collection of 
the sample, at the Plant Introduction Station at Brooksville, Fla. 
The differences in nematode content 
between the different depths in the same 
spot in the field are within a reasonable 
degree reliable. The regions of maxi¬ 
mum infestation, in the different spots, 
as determined by samples taken at 
different times, therefore, are roughly 
comparable. These regions were, on 
the whole, several inches beneath the 
surface. In June the nemas were most 
have been less numerous throughout 
the soil than in the summer months, as 
might very well be expected. During 
that period the temperature was below 
that shown by experiment to be favor¬ 
able for infection and development, and 
probably a large proportion of the 
many free larvae and eggs may have 
succumbed to the many unfavorable 
conditions to which in all probability 
