10 THE CONTROL OF APPLE BITTER-ROT. 
which rupture the skin and give forth pink masses of conidia, or sum- 
mer spores. (See Pl. II, 6.) | 
Summer spores.—lt is thought to be chiefly by means of summer 
spores that this fungus is propagated and disseminated, and countless 
millions of them may be produced from one rotton spot. They are 
produced one after another by abstriction from the ends of the fruiting 
branches of the fungus, and, as previously explained, exude through 
the ruptured skin of the apple in pink, sticky masses easily visible to 
the naked eye. They are readily washed off by the action of dew and 
rain, but upon drying become hard and glued to the skin of the apple. 
A microscopic examination shows these spores to be oblong, almost 
cylindrical, one-celled bodies with a delicate pale-green color and gran- 
ular contents. They vary in size, as also in shape, but normally 
measure 4-5X10-15 w. (Pl. I, 4, a:) 
Ascospores.—In addition to the conidia, or summer spores, which 
are produced so rapidly and in such great numbers, another type of 
spore is produced on the old rotten apples in the autumn and probably 
also the following spring. ‘These ascospores, measuring about 5 x 20 
(Pl. II, 2), are scarcely distinguishable from the summer spores, 
but are usually slightly curved and are borne in little sacs containing 
8 spores each. These sacs, or asci (Pl. I, 7), are produced inside 
of little brownish spore cases (perithecia) embedded in black nodules 
of mycelium on the surface of the rotten apple or mummy. This con- 
stitutes the mature stage of the bitter-rot fungus as first discovered by 
Clinton,“ and is probably a means of carrying the fungus over winter 
and starting infection the following spring. Von Schrenk and Spauld- 
ing? found it on limb cankers as well as in artificial cultures. The 
writer secured this stage of the fungus on a number of artificially 
infected apples in the laboratory about three weeks after inoculation, 
and it developed on a few rotten apples brought in from the orchard 
and placed ina moist chamber. It also developed abundantly in arti- 
ficial cultures on sterilized potato and nutrient agar within six weeks 
after inoculation. 
Germination of the spores.—Placed in a drop of water under a 
microscope, both conidia and ascospores may be seen to germinate 
within three or four hours, each spore throwing out one or two, some- 
times three, germ tubes. (Pl. Il, 3 and 5.) During germination a 
cross septum usually develops in the center of the spore, which soon 
becomes emptied of its contents. These germ tubes grow very rapidly, 
reaching several times the length of the spore within an hour after 
germination, and then begin branching. 
There is some question as to how the threads from the germinating 
@Clinton, G. P. Apple Rots in Dllinois, Bul. 69, Ill. Agr. Exp. Sta., 1902, pp. 
206-211, Pl. J. 
6 Bul. 44, Bureau of Plant Industry, U. 8. Department of Agriculture, 1903. 
