10 THE CONTROL OF APPLE BITTER-ROT. 



which rupture the skin and give forth pink masses of conidia, or sum- 

 mer spores. (See PI. II, 6.) 



Summer spores. — It 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 previoush' explained, exude through 

 the ruptured skin of the apple in pink, stick}" masses easily visible to 

 the naked eye. They are readily washed off b}" 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. The}' vary in size, as also in shape, but normally 

 measure 4-5x10-15 yw. (PI. II, 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 >w 

 (PI. II, ^), 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 (PI. II, i), 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 artiticial 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 in a moist cham])er. It also developed abundantly in arti- 

 ficial cultures on sterilized potato and nutrient agar within six weeks 

 after inoculation. 



Germination of the sj>orex. — 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. (PI. II, -i and 5.) During germination a 

 cross septum usually develops in the center of the spore, which soon 

 becomes emptied of its contents. These germ tulles grow very rapidly, 

 reaching several times the length of the spore within an hour after 

 germination, and then begin liranching. 



There is some question as to how the threads from the germinating 



"Clinton, G. P. Apple Rots in Illinoip, Bnl. 69, 111. Aorr. Exp. Sta., 1902, pp. 

 20&-211, PI. J. 



^ Bui. 44, Bureau of Plant Industry, U. S. Department of Agriculture, 1903. 



