266 PLANT DISEASES 



and afterwards secrete turpentine in considerable quantity, 

 which escapes through cracks in the bark. As the disease 

 encroaches on the wood, the upward passage of water is 

 checked, and the upper branches die, and are known as 

 ' resin top ' or ' resin leader.' 



The aecidia appear in late spring, bursting through the 

 outer dead cortex as irregularly shaped, pale yellow sacs, 

 which open by an irregular fissure, and liberate the powdery 

 spores. 



Hartig considers that the trunk cannot be infected after 

 the age of twenty-five years. How inoculation is effected 

 is not known, neither is the teleutospore form of the 

 fungus; consequently the only remedial measure that 

 can be suggested is the removal of diseased trees. 



Hartig, Wichtige Krankh. d. Waldbdumen. 



Tubeuf and Smith, Diseases of Plants (Engl. ed.), 

 p. 411, figs. 



Peridermium coruscans^ Fr. This fungus is common on 

 spruces in Northern Europe, and I have seen it on Abies 

 pinsapo in England. The whole of the leaves on a young 

 shoot are attacked, becoming shorter and succulent, and 

 such branches are eaten in Sweden. 



The peridia usually occupy the whole length of the 

 leaf, rupturing irregularly and exposing the bright yellow, 

 powdery spores. 



Peridermium conorum, 'Thum.=j4ecidiur/i conorum-piceae^ 

 Reess. The aecidia are large, appearing on the outer 

 surface of cone bracts of the spruce, few in number (but 

 not constantly two). 



Peridermium elatinum, Wallr. This species grows on 

 silver firs, forming cankered swellings on the trunk and 



