234 PHYTOPATHOLOGY [VOL. 6 



The inspection of the infected trees on March 25, 1915 gave the follow- 

 ing results: 



Of the seven inoculations on tree No. I five had taken, four of which 

 had produced well-defined aecia; two of these, on one-year twigs, pro- 

 duced slender barrel-shaped swellings, encircling the entire twig (one with 

 an aecial row, about 7.5 mm. long, in the axis of the swelling; the other 

 without an aecium, resin drops present in several places). Of the re- 

 maining three infections, one is represented by the photograph (figure 1) ; 

 the swelling is of slender barrel shape. The aecium measures 1| by 3 

 mm.; the swelling itself measures 3 em. in length by 1.2 cm. in diameter 

 as against 0.6 cm. of the stem immediately below. Another infection 

 caused a gall to form around about one-half of the circumference of the 

 stem; it bears a large aecium in the center. The third infection on the 

 lower part of the stem (at least 3 years old) resulting in a gall about three- 

 fourths around the circumference, has a small aecium in the center. The 

 exact ages of the stem and twigs at the various places of infection could 

 not be determined because the plant was kept for further observations. 



As to the two unsuccessful inoculations, it will be remembered that in 

 two cases the spore material had not been protected by cotton and paper 

 and had probably dried up. 



The control plants III and IV were in perfect health without a sign 

 of Peridermium harknessii. All parts of plant I not inoculated remained 

 sound. At the present time (December, 1915) the galls have grown 

 considerably; the check plants and all not inoculated parts of tree I are 

 perfectly sound. 



The period of incubation as figured from the time of inoculation to the 

 first manifestation of the effect of infection, in this case, of the swelling, 

 must be about four to five months. The first appearance of aecia in 

 the experiments took place about twenty months after inoculation. In 

 nature, the first swelling appears in the fall of the year of infection. Dur- 

 ing the next year the young gall remains stationary or grows but little. 

 In the spring of the third year, the aecia develop and sporulation begins. 



In the experiments the one-, two- and three-years-old stems and twigs 

 proved susceptible to infection; none were made on twigs younger than 

 one year, because at the time of experimentation the buds had not yet 

 sprouted sufficiently. In nature, infection of stems older than two years 

 must be rare, at least no infection on older stems could be found in spite 

 of careful examination of the great number of galls. Infection of twigs 

 during their first year of growth, on the other hand, is frequent. Investi- 

 gations of this kind must, of course, be made in spring, because the result 

 of spring infection begins to show towards fall of the same year. 



