WHITE-PINE BLISTER RUST. 27 
infection of young plants he attributes to the fact that shoots bearing 
primary (juvenile) leaves go into the winter season with buds at all 
stages of growth, and many are incompletely protected by bud 
scales. Inoculations made on September 11, 1914, with sporidia 
succeeded on the primary leaves, on the secondary (mature) leaves, 
and on the epidermis of growing buds and of young shoots. Yellow 
spots were present on all these parts in the spring of 1915. 
Chnton and Miss McCormick (12, 14, 15) have recently announced 
successful inoculations in the leaves of Pinus strobus. Studies of 
thousands of infections show that infection takes place through the 
stomata of the pine leaves of all ages. Inside the stoma a sub- 
stomatal vesicle is formed which is of a characteristic shape. Thence 
the mycelium extends into the vascular bundle and then grows rapidly 
downward to the twig. Infection may take place in 48 hours. 
Inoculations on stems did not succeed. Inoculations on opened 
and unopened buds succeeded in a few cases, results being somewhat 
doubtful with the unopened ones. Infections on the leaves become 
visible, about a month after inoculation, as tiny yellowish spots 
centering on the line of stomata on the under side of the leaf. These 
spots turn golden yellow. Similar yellow spots may form on the 
twig after the fungus has become established there. A yellow 
mottling of the infected leaves is the principal symptom of the disease 
at this time. 
This is rarely noted in nature, but two instances having been seen 
by the writer before 1920 (131, 132, 133, 134). The spots were on 
both leaves and stems of naturally infected Pinus strobus trees. 
Richards has recently found them on naturally infected leaves. 
So far as known they have been mentioned previously only by 
Tubeuf (174); Klebahn (71), who noted them on artificially infected 
trees but failed to designate the point of infection; and by Pechon 
(105), who observed them on naturally infected trees. The writer 
thought the yellow spots resulted from the growth of the fungus out- 
ward from the stem into the leaves. Klebahn seems to have been 
of the same opinion. It is believed that this happens sometimes. 
In 1920 such spots were seen on pine leaves naturally infected at 
Temple, N. H., and at New Boston, Mass. They are abundant in 
certain localities. Artificial infections have resulted from inocula- 
tions into the bark of the stem by the writer (133). 
Cronartium ribicola is able to grow in bark much more than 3 or 
4 years old if it once gains access to the interior. Infections have 
been seen which were still producing secia on bark up to 35 years 
of age. A common method of infection of pine trunks 20 or more 
years of age is by growth of the mycelium from infected small side 
branches (135). (PL II, figs. 1 and 3.) Very often a twig near the 
base of a large branch becomes infected. The disease then extends 
