1256 
Joumal of Agricultural Research v 0 i. xxvm, No. 12 
SEVERITY OF INFECTION IN PINE STANDS OF DIFFERENT DEGREES OF 
STOCKING 
In different units of the area, similarly exposed to Ribes, the percentages of 
infected trees varied according to the degrees of pine stocking. The percentages 
of infected trees were highest in understocked stands and lowest in overstocked 
stands. Figure 3 shows the percentages of trees infected in stands of the area 
having different degrees of pine stocking. 
PINE INFECTION SURVEY, 1921 
In 1921 an inspection was made of the entire experimental control tract at 
Kittery Point, where the Ribes eradication work had been done in 1917, to 
ascertain the effectiveness of this work in preventing further infection of the pine. 
No pine infection occurring since 1916 was found except in isolated portions of 
INFECTION PER CENTS IN STANDS OF DIFFERENT DEGREES OF PINE' STOCKING 
PER CENT or 
TREES INFECTED 
Fig. 3.—Compiled from the data on the west half of the experimental area shown in fig. 1 
the tract where an occasional Ribes bush had been missed by the eradication 
crews or new ones had grown since 1917. Detailed investigations were made 
on thirty-two ^-acre plots located in the experimental area where all of the 
Ribes bushes had been destroyed in 1917 and no new bushes, had grown since 
that time, to determine the condition of the pines and the changes which had 
taken place in the stands. 
On the 32 plots there remained 1,737 trees of the original stand studied in 1918 
Of these, 31 per cent or 546 trees had been killed by the blister rust as a result 
of infections which occurred prior to the eradication of Ribes. Painstaking 
examination of the remaining 1,191 live trees of the original stand and 485 young 
trees that had seeded in on the area since 1917 showed that no new infections 
had occurred since 1916. 
There was a marked variation in the severity of infection of different crown 
classes (fig. 4.) The dominant trees, which are of greatest economic importance 
in the stand, were subject to the highest degree of infection from blister rust. 
