250 DISEASES OF CULTIVATED PLANTS 



by wet summers and mild, damp winters. Attacked seedlings 

 usually die, and can only recover when about half the 

 number of leaves remain healthy. 



The ascophores are scattered on pale spots on the leaf, 

 shining black, up to i mm. long ; asci clavate, 8-spored, 

 spores nearly as long as the ascus, 90-1 20 X 1*5 /*. 



Conidia cylindrical, colourless, continuous, 6-8 x i /* 

 Called Ltptostroma pinastri (Desm.) 



On leaves of Scotch fir and other conifers. The leaves 

 of old trees are also attacked. 



To secure seedlings free from disease the seed-beds 

 should be formed at a distance from infected areas, otherwise 

 the spores may be carried by wind or other agents. Where 

 tracts have been devastated by the disease, the trees should 

 be replaced by Weymouth pines, which are immune. 



Hartig and Somerville, Text-Book of Diseases of Trees, 

 (Engl. ed.), p. no (1894). 



DICHAENA (FRIES.) 



Ascophores crowded and forming extended black patches, 

 rounded or elongated, opening by an elongated slit ; asci 

 obpiriform or broadly fusiform, 4-8 spored; spores septate, 

 hyaline; paraphyses slender. 



True parasites on living bark, but do little or no injury. 

 Often sterile. 



Oak bark blotch. The flat, rough black patches varying in 

 size from i to 3 cm., so common on the bark of living oak 

 branches, are caused by Dichaena quercina (Fries.) 



Two forms of pycnidia are first produced which resemble 

 the ascophores in form. One contains myriads of hyaline, 

 elliptical spores about 5X3^. The other produces larger, 

 broadly elliptical hyaline spores, borne singly on slender 

 pedicels, 22-25x8-10 p. Asci broadly piriform, sessile, 

 8-spored; spores elliptical, hyaline, i- then 3-septate (said to 

 become muriform), 21-25 X 8 p. 



Dichaena faginea (Fries.), which resembles D. quercina in 

 appearance, grows on smooth living beech bark. 



Other species or varieties of similar appearance occur on 

 bark of hazel and goat willow. 



