— i8o — 



were placed upon it. The evidence, therefore, is in favor of the 

 above hypothesis ; and as numerous conidia are produced from the 

 mycelium growing from one ascospore, the fungus is enabled to in- 

 crease many fold the effectiveness of its attack. 



Several authors have indicated by figures and descriptions the 

 development of mycelia and basidia from the surface-cells of the 

 perithecium, particularly about the ostiolum. These were said to 

 bear conidia, indistinguishable from the sunnner or the sclerotium 

 conidia. Although especially sought for, no such out-growths 

 were observed arising from the walls of the perithecium. The fact 

 that the ascospores naturally germinate within the perithecium, 

 and the mycelial filaments grow not only out of the ostiolum, but 

 burst the wall of the perithecium, and grow through its rents, led 

 to the conclusion that observers may have been, in some cases, 

 deceived by the out-growth, supposing it to be directly from the 

 wall-cells of the perithecium itself. 



CONDITIONS AFFECTING THE DEVELOPMENT OF THE BLIGHT. 



It has been intimated in the early part of this discussion, that a 

 wet May or June succeeded ])y a hot. perhaps dry, siunmer causes 

 the parasite to develop rapidly ; that the production of a large 

 crop of berries has frequently been followed by heavy, perhaps 

 fatal attacks of the Blight. '■= It might be added, tliat wet, un- 

 drained soil greatly favors it.f All these favoring conditions may 

 be reduced to, or result in a single one, namely, an unhealthy or 

 weakened plant. Ou the other hand a season either prevail- 

 ingly dry or with abundant moisture throughout, is quite 

 unfavorable to the development of the disease. There was 

 an enormous amount of the fungus in many fields in 1888, 

 and therefore an abundant supply of mycelium and spores, 

 both of which in the spring of 1889 developed vigorously 

 on the old leaves. But the leaves of this .season's growth 

 have been conspicuously free from the spots. This is true not only 

 of plants reasonably healthy last year, but of beds where the leaves 

 of last year still bear witness of the great ravages at that lime. 

 The Wilson very susceptible to the disease, and the Sharpless 

 supposed to resist it more or less successfully, are both quite free 

 from it in this vicinity. The season has had an abundant rainfall. 



* J. M. Smith, Second Ann. Report Wise. Agr. Kxper. Sta., p. 56, says : 

 " Four-fifths of the plants (in a certain field) were dead from rust ; and that, 

 just as far as they had borne heavily but no farther." 



t Scribner, 1. c, p. 336. 



