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 primar}^ leaves, on the secondary (mature) leaves, 

 and on the epide^rmis 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 annoimced 

 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 yeUow 

 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 wi'iter 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); ICebahn (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 wi'iter 

 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 locahties. 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). (PI. II, figs. 1 and 3.) Very often a twig near the 

 base of a large branch becomes infected. The disease then extends 



