Blister Canker 
37 
During the winter of 1916-1917 a number of two-year-old 
trees were planted in large jars in the greenhouse. A group 
of 10 were inoculated just as soon as set, 10 more four weeks 
later just as the buds were swelling, and an equal number 
as soon as the trees were in full leaf, which was about five 
weeks after the second series. They were examined fourteen 
weeks after the first inoculations were made. The average 
growth in the first series was 18.75 inches above and 20.75 
inches below the inoculations, or a total of 49.5 inches. This 
was an average of slightly over 3.5 inches per week. The sec- 
ond series made an average growth of 8.2 inches above and 
9.5 inches below, or a total average of 17.7 inches. This was 
an average of 1.77 inches per week. The third series made 
when the trees were in full leaf showed an average growth of 
1.37 inches above and 1.45 inches below, or a total average of 
2.82 inches. This was an average of 0.56 inch per week. The 
data thus far indicate that the mycelium makes its most rapid 
progress during the season when the tree is making little 
growth. Whether the slow growth is due to the retarding 
influence of an abundance of water and a lack of air or 
whether rapid growth is due to the presence in the tissues of 
stored food materials, the writer has been unable to deter- 
mine. 
EFFECT OF SOIL ^lOISTURE ON SUSCEPTIBILITY 
An effort was made to ascertain the relation of the amount 
of moisture in the soil to susceptibility to blister canker. Oil 
barrels were secured and sawed thru half way between the 
heads. Each end made a large tub. The oil was burned out 
and the tubs set in the ground so that only about three inches 
of the top remained above the surface. The trees were planted 
in soil in these tubs which were covered with a flat cone of 
rubberoid roofing to exclude rain. Water was prevented from 
running in at the hole around the tree trunk by a shield of 
potter's clay. 
In one series the soil was kept saturated, in another the 
water content of the soil was kept at the optimum for normal 
growth, while in the third only enough water was supplied to 
keep the trees from dying. 
In the saturated series all of the trees soon died so that no 
data could be secured. The data from the other series are 
given in table 10. 
There was considerable variation in the individual trees 
of the same series, and in several cases trees with an optimum 
