54 THE BITTER ROT OF APPLES. 



Plate VI. Fig. 1. — A pure culture on apple agar, showing the luxuriant develop- 

 ment of the bitter-rot fungus, with large numbers of spores. After a time this 

 spore production stops and peculiar hard black masses develop. These masses 

 are shown in Fig. 1. From a number of them large drops of a yellowish liquid 

 are exuding. Each black mass contains one or more perithecia of the bitter-rot 

 fungus, with asci, such as are shown on Plate V, rig. 6. Fig. 2. — Enlarged group 

 of pustules on a diseased apple. On quiet, moist nights the spore masses of the 

 bitter-rot fungus exude .from the mouths of the pustules on the apple fruit in 

 long filmy threads. Some of these threads, composed wholly of spores, are 

 shown exuding from some of the pustules. Figs. 3 and 4. — Apple diseased with 

 bitter rot and control fruit. These figures show the result of an experiment to 

 determine whether the spores found in the apple cankers would produce the 

 bitter rot in apples. A pure culture was made with spores taken from an apple 

 canker. Spores from this pure culture were inoculated into an apple- (rig. 3), 

 while another apple was punched full of holes with a sterilized needle. As 

 shown in the figures, the inoculated fruit (fig. 3) developed a typical case of the 

 bitter rot, while the control fruit (fig. 4) was still sound. This is one of- 

 numerous proofs that spores from the apple cankers produce the disease. 



Plate VII. Three typical cankers such as are now believed to be formed on apple 

 limbs during one stage in the life cycle of the bitter-rot fungus. Spores from 

 these cankers produce the bitter rot of apples. Such cankers should be cut out 

 and burned wherever found. 



Plate YIII. Cankers on living apple limbs. Fig. 1. — A number of cross sections of 

 apple cankers, illustrating the manner in which the wood turns brown immedi- 

 ately under the dead bark. It also shows the healing callus forming at the edge 

 of the. dead areas.' The largest section shows two such healing layers, proving- 

 that this canker is at least two years old. Figs. 2 and 4. — Apple branches, fig. 4 

 showing probably early stages of canker. Fig. 3. — A branch swollen at the 

 point where an apple was borne the previous year. Many such were found to 

 contain bitter-rot spores. It is possible that the fruit spurs became infected 

 from diseased fruits through the stems of the apples. 



Plate IX. Young apple cankers produced by inoculating spores from pure cultures 

 of the bitter-rot fungus into bark slits on healthy apple trees. In all cases here 

 shown small cankers were formed, pustules with spores developed, and the 

 spores, when inoculated into apples, produced the bitter rot of the fruit. This 

 formed the last link in the chain of evidence necessary to show the connection 

 between the bitter-rot fungus and the apple canker. 



o 



