DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 513 



thoroughly. So it has been with the black-rot fungus. The pycnidial 

 stage on the grape leaves (Fig. 185) was called Phylloslicta labrusca, 

 while on the fruit it was called Phoma uvicola. These have been 

 determined to be merely stages of one and the same fungus, Guignardia 

 Bidwellii. The mycelium of the black-rot fungus is never abundant in 

 the outer portions of the berries where it is found. Here a stromatic 

 mass of hyphae arises beneath the grape skin and develop the pycnidia, 

 which are broadly elliptic, thick-walled and 

 beakless depressions from the inner walls of 

 which the pycnidiophores arise which abstrict 

 off the ovate to elliptic pycnidiospores (pycno- 

 spores) 8 to loy. by 7 to 8/i. These are pushed 

 out in twisted masses and can germinate im- 

 mediately. 



Spermagonia-like pycnidia of smaller size 

 are also found. These produce filiform con- 

 idiophores, which cut off minute, slightly 

 curved microconidia. The ascigeral stage, 

 discovered in 1880, may be had on fruit, 

 which has been covered with grass and leaves 

 in the dried up state. The perithecia are 

 globose and bear broadly clavate asci con- 

 taining eight unicellular ascospores, measur- 

 ing 12 to 17/i by 4.5 to sn. 



The black-rot grape disease can be con- 

 trolled by Bordeaux mixture (4-4-50). The ^:,^^^;;;^^-^, 

 first application should be made in the spring, attacking green grapes. Cold 

 just as the buds begin to swell, followed by ^^^^f^^f^'^°'- ^- ^- ^"'^ 

 a second spraying, as the buds unfold. Sub- 

 sequent sprayings, always before rain storms, to the number of five 

 or six, should be made two weeks apart during the season. After 

 July 20 use 4-2-50 Bordeaux, or ammoniacal copper carbonate. 



Downy Mildew (Plasmopora viticola (B. & C.) Berl. & DeTon).— 

 The consensus of opinion among mycologists is that the downy mildew 

 fungus is of American origin, and it is now widely spread in Europe and 

 eastern North America, where it probably did not originate. It has 

 been noted on practically every variety of cultivated and wild grapes, 

 and it attacks stems, leaves and berries. Usually it confines its attack 

 33 



