322 DISEASES OF CULTIVATED PLANTS 



Diseased plants should be removed, as the mycelium is 

 perennial and they always remain infected, and in addition 

 are liable to infect healthy plants. 



PERIDERMIUM (LEV.) 



Aecidia growing on bark, cone-scales, or leaves, erumpent, 

 saccate or tubular; spores in chains, globose or elliptical, 

 orange; spermogonia truncato-conoid. Uredospores and 

 teleutospores unknown. 



Peridermium harknessi^ Moore (Peridermium filamen- 

 tosum, Peck), often proves very destructive to Pinus ponderosa 

 growing on the Sierra Nevada mountains. It attacks the 

 young tree trunks and arrests further growth. The parasite 

 also attacks the following trees in North America; Pinus 

 insignis, P. sabiniana, and P. contorta. Specimens sent to 

 Kew by the late Dr. Harkness, from Sacramento, California, 

 showed that the fungus had first attacked the stem when two 

 or three years of age, and in one specimen the perennial 

 mycelium had continued to grow year by year until the tree 

 was thirteen years of age, when the specimen was collected. 

 During this period of growth the fungus had caused the 

 stem at the point attacked to assume a barrel shape, four 

 inches long and three inches in diameter. The stem just 

 below the swelling was one and a half inches in diameter. 



Pseudoperidia crowded, irregular, large, growing all round 

 the branch, aecidiospores irregular in form, orange, at length 

 whitish, 35-40 p diam., very minutely echinulate. 



Peridermium coruscans (Fr.) is common on the spruce 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. Such branches 

 are eaten in Sweden in times of scarcity. The peridia 

 usually occupy the whole length of the leaf, rupturing 

 irregularly and exposing the bright yellow, powdery spores. 



Pseudoperidia numerous, longitudinally arranged, at first 

 closed, ellipsoid, then membranaceous, elongated, whitish, 

 tubular, apex divaricating, pale red ; spores usually globose, 

 orange-yellow, 30-35 X 20-24 / z > epispore thin, obscurely but 

 very densely verruculose. 



Peridermium orientals (Cooke) grows on the leaves of 

 Pinus longifolia and P. excelsa in the neighbourhood of 



