24 THE BITTER ROT OB" APPLES. 



is covered with a dense growth of mycelium after a period of from 

 ten to fourteen days. At about the time when the conidia cease to be 

 formed small black knots appear among the tangled mass of hyphae, 

 looking much like warts. Drops of a yellowish liquid frequently 

 exude from these black bodies (PI. VI, tig. 1) The latter increase in 

 size and frequently form masses one-fourth of an inch in diameter. 

 Cultures on apple agar will show good-sized masses of this kind in 

 from twelve to eighteen days. These black masses contain the peri- 

 thecia of the bitter-rot fungus. 



The perithecia and asci were first described by Clinton (1902), who 

 proved their connection with the bitter-rot fungus (Glceosporium jruc- 

 tigenum Berk.) by inoculating ascospores into apples and producing 

 the bitter rot. The formation of perithecia was found by the writers 

 to occur with great constancy under appropriate conditions. As a 

 rule the perithecia form in older cultures only. 



The black nodules in which the perithecia are embedded are hard 

 masses of mycelium, which may be characterized as carbonaceous. 

 They are very irregular in shape and vary in size from a small pin 

 head to one-fourth of an inch in diameter. The perithecia. from one 

 to many, are embedded in this carbonized mass. In apple-agar cul- 

 tures the perithecia form when the black nodules are still very small. 

 When there is but one perithecium in a nodule it is almost spherical; 

 when there are several, they are somewhat flattened laterally, and 

 sometimes very irregular in form. There is no beak. Clinton (1902) 

 found the perithecia to be from 125 to 250 m in length. These meas- 

 urements ag-ree fairly well with those found by the writers. The 

 walls of the perithecia show marked reticulations about 6 to 14 /< in 

 diameter. These are quite marked in the early stages, but become 

 obscured as the perithecium matures. 



The asci (PI. V, fig. 6), which occur in considerable numbers in a 

 perithecium, are oblong-clavate in form, 55 to 70 m by 9 /<, often with 

 a slight pedicel, and are comparatively thin walled. When mature 

 they break open and disappear rapidly. They contain 8 ascospores, 

 which are usuall} T arranged in pairs, more rarely in oblique series. 

 The spores resemble the conidia formed directly on the mycelium, so 

 much so that they might easily be taken for conidia. They are per- 

 haps curved a little more than the conidia, a character which can some- 

 times be used to separate the two, but not always. The ascospores 

 and the conidia are about the same size, though the former are not as 

 variable as the conidia, measuring 12 to 22 /< by 3.5 to 5 //. Their 

 great resemblance has probably led to the ascospores remaining undis- 

 covered for so many years. The asci are short lived and after they 

 have discharged the spores they vanish. When found in apples it is 

 practically impossible to tell whether any particular spore is an asco- 

 spore or a conidium. The ascospores germinate much in the same 



