478 SPECIAL PLANT PATHOLOGY 



been discovered. The gleosporial, or imperfect stage, usually develops 

 on the fruit, while the ascigeral stage is occasionally produced on a 

 fruit or twig, and in artificial cultures is readily obtained. Early in- 

 fection of the fruit is probably due to the spores produced in pustules 

 on the areas of stem, which have become cankered through the attack 

 of the bitter-rot mycelium. Such cankers are sunken areas upon twigs 

 or limbs, accompanied by a cracking and breaking of the bark over such 

 regions. The pustules, which accompany the rot of the fruit, are formed 

 beneath the apple skin as ccmdensed masses of the mycelium known 

 as stroma and these emerge as a cone-shaped mass of erect hyphae, 

 which are the conidiophores, which cut off conidiospores that emerge 

 as a pink waxy strand, later becoming of a gray color. The ovate to 

 oblong conidiospores, which measure in extreme cases 6 to 40 by 3.5 

 to 7/1, more usually 12 to 16 by 4 to 6/i, are imbedded in a gelatinous 

 matrix which dissolves in water setting the spores free. These spores 

 germinate freely and become septate in doing so. Infection of apple 

 fruits may be through the uninjured skin, but a slight abrasion facilitates 

 the entrance of the germ tube of the spore. Berkeley, who first 

 described this stage, named it Gleosporium Jructigenum and under this 

 scientific name the disease is frequently quoted. 



Clinton discovered the perithecial stage in 1902, and as it is readily 

 obtained in cultures on any of the ordinary nutrient media its character- 

 istics are well-known. The perithecia which are developed contain 

 oblong-clavate asci, 55 to 70 by g/x, which develop eight curved asco- 

 spores, usually uniform in size, 12 to 22 by 3.5 to 5/1. The pomologist, 

 who wishes to control the disease, should prune away all cankered limbs 

 and keep the orchard free of diseased fruits. The spraying of the trees 

 with Bordeaux or lime-sulphur (3-3-50) has been found efficacious, 

 and the crop returns from sprayed trees, as contrasted with unsprayed 

 trees, have abundantly repaid the trouble which the orchardist has 

 taken in the application of Bordeaux mixture. The first application 

 of the spray should be in the form of a mist about a month after the 

 petals have fallen and subsequent applications should be made about 

 two weeks apart until at least five sprayings have been made. 



Black-rot {Spharopsis malorum Berk.). — Although the apple is 

 one of its host plants, the black rot fungus attacks other pomaceous 

 trees, producing cankers so that the description of the disease and 

 fungus, as applied to the apple, will serve with certain modifications for 



