332 



Bulletin 263. 



table parasite and is so small that it cannot be seen except with the 

 aid of a compound microscope. 



When one examines the diseased part of a stem microscopically, he 

 can find in and between the cells of the wood extremely minute cobweb- 

 like threads called mycelium. 

 This mycelium constitutes the 

 vegetative part of the fungus. 

 It feeds on the substance of the 

 wood cells, and other parts, grad- 

 ually destroying them and pro- 

 ducing a dry rot. 



The fungus may vegetate for 

 several years and its presence in 

 the stem sets up an irritation in 

 the living tissue. The vine is ex- 

 cited to excessive growth in cer- 

 tain regions as though it were try- 

 ing to throw off the irritant. This 

 excessive growth is manifest to the 

 eye as large, tumorous swellings 

 (Figs. 45, 46, 47), or fleshy,, 

 longitudinally-ribbed excrescences 

 (Fig. 44). As the sap tubes 

 are slowly attacked and killed, 

 the amount of water that reach- 

 es the leaves and growing parts 

 becomes less and less. This causes 

 a dwarfing of the shoots and 

 blanching of the leaves. Often, all 

 the leaves cannot be supported and 

 some turn yellow and die. For the 

 same reason, fruit buds are 

 developed sparingly and the fol- 



Fhoto. June 27, 1908 

 Fig. 48. — Niagara. Lesions of the 

 disease on green shoots 



lowing year the vine either fails entirely to set fruit, or the setting is 



light. 



When the fungus has encroached far enough upon the living tissue 

 completely to cut off the sap supply, the vine dies. This may happen 



subfusoideis, continuis, hyalinis, rectis vel leniter curvis, 6.3 — 11.2x1.7 — 2.8; 



basidiis longibus, crassis paraphysibusque filiformibus, longioribus inter- 



mixtis. 



Hab. in ramis truncisque exsiccatis Vitis labruscae et rotundifolii vars. 



