POLYPORUS SULPHUREUS. 475 



hibernate, which the ordinary mycelium cannot do. The 

 disease is also perpetuated by conidia springing from the 

 portions of the mycelium growing above ground, or by spores 

 produced either from the sub-aerial portion of the oak-plant 

 or in the ground, these as a rule only germinate in the year 

 following that of the original infection. 



b. Subjects of Attack, and Distribution. 



This fungus is very dangerous in seed-beds and dense sow- 

 ings in the open up to 2,600 ft. altitude, especially in wet 

 years. It is common in North-West Germany, also in Wiirt- 

 temberg, where, in 1890, it killed 100,000 13 years old 

 seedlings. 



c. Protective Rules. 



i. Places where the fungus has appeared should be isolated, 

 by digging trenches one foot deep to prevent the spread of the 

 rhizomorphs. 



ii. Plants which have been attacked must be at once 

 removed and burned, which can always be done in nurseries. 



B. Stem and Branch Fungi. 



2. Polyporus sulphureus, Fr. 



This widely-distributed fungus, which is very common in 

 the British Isles, and has been already referred to as attacking 

 the larch and silver-fir, destroys the wood of oaks, sweet 

 chestnut, poplars, tree-willows, alders, birch, etc., and fruit- 

 trees. 



The infection occurs at wounds in the branches of trees ; 

 the wood, in consequence, turns reddish-brown, cracked and 

 dry, the mycelium spreading through the cracks and forming 

 large felted white sheets, it also fills the vessels, which on the 

 different sections of the wood appear like white lines or 

 points. At the scars of dead branches, or other parts of the 

 stem, large sulphur-yellow, fairly smooth, fleshy sporocarps 

 appear annually which are somewhat reddish above and very 

 conspicuous. 



All infected trees should be felled if this does not open out 



