186 



ASCOMYCETES. 



The dark-red masses of thick-coated, warty perithecia appear 

 in autumn and winter on the dead branches only ; the asci 

 contain eight bicellular hyaline spores which germinate 

 directly to form a mycelium. Infection of a new host-plant 

 is effected by the mycelium, which enters by open wounds into 

 living branches ; it is quite unable to penetrate the living 

 bark and is dependent on wounds. The mycelium spreads 



rapidly through the tissues of 

 the host, especially through the 

 vessels of the wood ; the cam- 

 bium and' rind are not attacked 

 directly, but are killed in conse- 

 quence of the destruction of the 

 wood. 1 The regions attacked 

 in the wood appear as greenish 

 stripes, and withering of leaves, 

 followed by death of branch 

 after branch, results in conse- 

 quence of the growth of mycelium 

 in the water-conducting elements 

 of the wood. 



For protection against this 



^^^ and all other parasites, which 



find entrance by wounds, it is recommended to prune or dress 

 trees only when necessary, and to paint all wounds with tar 

 or tree-wax. This Nectria is one of the commonest parasites 

 of our parks and fruit gardens, hence all branches already 

 attacked should be removed and burned, likewise all blown 

 timber which might serve as a nursery for production of 

 spores or conidia. 



Nectria ditissima Tul. (Britain and U.S. America). This 

 is a common parasite and a frequent cause of the canker of 

 beech, apple, and other trees. 2 The mycelium lives chiefly 

 in the bark, causing it to die and form cracks. Under 

 ordinary conditions all cracks and fissures are occluded or 



1 Mayr in Hartig's Untersuchungen a. d. forxt-botan. Institut zu Mihichen, in. 

 Berlin, 1882. Brick, Arbeiten d. hot an. Muwum*, Hamburg, 1892. 



Wehmer (Zeitxch. f. Pftanz'-nkrankheiten, 1894 and 1895), opposes Mayr's con- 

 clusions and holds that Nectria can penetrate intact, living bark. 



-Goethe, " Ueber Krebs d. Apfelbaume." Rhtiii. Blatt f. OW. , Wciii, it. Gar- 

 i< nl>mi, 1879. R. Hartig, Untersuch. aus d.forst-botan. Institut. zu Miinchen, i. 



Fir;. 79. Nectria cinnabarina. Enlarged 

 section of perithecial colony. Germinating 

 ascospores. (After Tulasne.) 



