FRUIT BLOTCHES. 9 



Sheldon a reported observations which had led him to the same con- 

 clusions, and in addition he identified the fungus as Phyllosticta 

 solitaria E. & E. Stevens b later in the same year recorded the 

 canker form of the disease from several localities in Xorth Carolina. 



DESCRIPTION AND BEHAVIOR OF APPLE BLOTCH. 



Apple blotch occurs on the fruit, branches, and leaves. Although 

 the form on the fruit is by far the most important from an economic 

 standpoint, the twig cankers play an important part in the life cycle 

 of the fungus causing the disease. 



FRUIT BLOTCHES. 



The first evidence of the disease on the fruit is a very small, in- 

 conspicuous, light brown blotch which under a hand lens has the 

 appearance of a stellate collection of brown fibers just beneath the 

 epidermis. The blotch, spreading radially, increases in size, attain- 

 ing a" diameter of from one-eighth to three-eighths of an inch, 

 sometimes one-half an inch, and becomes darker in color. The ad- 

 vancing margin is irregular and jagged and has a fringed appear- 

 ance. On very young apples the points of infection occasionally 

 show as small water-soaked areas, and in wet weather there may be 

 a yellowish gummy exudation from the spots. Where the >pots are 

 numerous they often coalesce and form large blotches, which may 

 cover half the apple or more. The fungus kills only the superficial 

 cells (the epidermis and outer perenchyma). so that the continued 

 growth of the uninvaded tissues beneath results in a cracking of the 

 di.-cased areas. The cracks thus formed, though usually about half 

 an inch long, may girdle the fruit and extend to the core. The 

 cracks often intersect, forming a cross. The character of the spots 

 varies somewhat on different varieties. There are all gradations, 

 from those on the Missouri variety, which are quite large, much 

 fringed, and smooth, to those on the Limbertwig. which are small, 

 compact, and often umbonate. An occasional spot somewhat rec- 

 tangular in shape may be decidedly sunken and quite black, with a 

 definite margin. (See PI. I, figs. 1 and 2. and PI. II. fig. 2.) 



Within a few days after the spots become visible, black pycnidia 

 begin to develop on the diseased areas. Three or four to many occur 

 on each spot, and they may be -cattered promiscuously or grouped on 

 a small blister cracked around the margin. 



The general effect of the blotche- on the fruit is to mar its appear- 

 ance and render it unfit for packing. Moderately affected fruit, 

 especially if not badly cracked, may be evaporated, but much of it 



° Science, n. s., 26, No. 658, pp. 18&-185, August :». 1907. 

 b Science, n. s., 2(3, No. 073, pp. 724-Tiir,. November 22, 1907. 



144 



