SPRUCE LEAF-BLISTER. 



247 



June, they induce flow of resin, the growth of the tree is interfered with, 

 and often the whole tree above the infected part dies. The mycelium 

 hibernates, but increases year by year, as also the cankerous parts, and in 

 course of time the crown dies, though young poles are often killed during 



Fig. 64. 



Twig of Spruce attacked by Chrysomyxa abietis. 3 to 4 times natural size. 



a, 6. First appearance of 

 pale yellow marks about 

 end of May or June. 



c. Long spore-pustules 

 formed during autumn. 



d. The bursting of a 

 spore-pustule in follow- 

 ing May. 



the first year, and especially in warm dry years. 

 The only way to prevent the disease spreading is 

 to cut out and remove infected poles as soon as 

 possible. The commonest alternative host-plant is 

 not yet known. 



Of the genus Chrysomyxa, the commonest species is the autoxenous 

 Spruce leaf-blister, Ch. abietis (Fig. 64, 65), on young Spruce foliage, and 

 mostly low down in 10- to 20-year-old plantations on wet soil and in damp 

 warm places, while 1-year-old or older leaves are immune, and the top of 

 the crown is little attacked. New leaves infected in any year become 

 speckled with pale yellow bands on 1 -year-old leaves in May or June of 



