Jan. 21. 1918 Irrigation Experiments on Apple-Spot Diseases 127 



as the C3,usal agency. They considered the disease of a physiological 

 nature and found that it could be partially prevented by early picking, 

 prompt cold storage, and early consumption after removal from storage. 



Norton (15) reported that spots practically identical in appearance 

 with the Jonathan-spot could be produced by the gases of ammonia and 

 folmaldehyde. 



Cook and Martin (5) considered Jonathan-spot to be a form of rot 

 caused by a species of Alternaria. In a later report (4) they made a 

 distinction between the small, nearly black, typical Jonathan-spots that 

 were more commonly confined to the dark area of the skin, and the 

 larger light-brown "Alternaria" spots that were more common on the 

 lightest area of the skin. They reported that they were able to reduce 

 the amount of the disease by keeping the apples covered with glassine 

 bags during the latter part of the summer, and considered that this 

 fact furnished further evidence that the spots were of fungus origin. 



DESCRIPTION OF JONATHAN-SPOT 



"Jonathan-spot" is the term applied to superficial black or brown 

 spots that are especially common on Jonathan apples. The trouble is 

 also found on Esopus, Yellow Newtown, Stayman Winesap, and other 

 varieties. In the early stages of the disease only the surface color-bear- 

 ing cells are involved and the spots are seldom more than 2 mm. in diame- 

 ter, but later the spots may enlarge to a diameter of 3 to 5 mm., become 

 slightly sunken and spread down into the tissue of the apple to a con- 

 siderable depth. In this later stage of the disease rot fungi are often 

 present, Alternaria being particularly common. 



EXPERIMENTAL WORK 



The Jonathan-spot experiments were carried out in the same Jonathan 

 orchard and on the same apples as the bitter-pit experiments, and the 

 details in regard to soil, irrigation, time of picking, and condition of stor- 

 age have already been given. 



In 1 91 5, plat 5 suffered severely from drouth the latter part of the 

 season, the trees finally losing more than three-fourths of their foliage 

 and the fruit becoming badly bronzed by the sun. Plats 2 and 3 also 

 became very dry in August but there was no defoliation. The soil moist- 

 ure conditions for the season are given in figure 7. The first picking was 

 made September 3. The fruit at this time lacked fully 10 days of being 

 at its best stage of maturity for picking. A second picking was made 

 on September 1 7 and a third picking on October i . The fruit of the last 

 picking was highly colored and dead ripe. 



There was no Jonathan-spot at picking time. The results of notes 

 taken on November 10 and February i are given in Table X. 



