16 THE BITTEK ROT OF APPLES. 



CHARACTER OF THE SPOTS. 



The first signs of the bitter rot appear in the form of a very faint 

 light-brown discoloration under the skin of the apple. The spots are 

 exceedingly small at first, and as they grow larger they appear cir- 

 cular in outline. (PL IV, fig. 2.) The spots rapidly increase in size, 

 becoming darker brown. When the spot is one-eighth of an inch in 

 diameter the area appears distinctly sunken. The borders of these 

 spots are usually very nearly circular and sharply defined. When 

 about one-half an inch in diameter small black dots appear at more 

 or less regular intervals beneath the epidermis in the sunken area. 

 These increase in size and project as tiny raised points. At a later 

 stage they break through the epidermis of the fruit and allow large 

 numbers of spores to escape. (PI. IY, figs 1 and T.) These spores, when 

 not washed from the fruit, form pink masses, sticky when moist. As 

 the spore mass dries it cakes and adheres to the epidermis. On quiet, 

 dry nights the spores are discharged in long tendril-like threads 

 (PI. YI, fig. 2), oozing out slowly from the mouths of the black 

 bodies, which are the fruiting bodies of the bitter-rot fungus. These 

 black bodies or pustules are often arranged in the form of a ring. 

 (Pis. I and II.) As the rot progresses other rings of pustules appear 

 outside of the first one, and at regular intervals six to eight, and 

 sometimes more. Avell-defined rings may form in rapid succession. 

 Each ring will have hundreds of pustules, each producing spores at 

 the same time, so that some rings appear almost continuous. (Pis. I, 

 II, and IY, figs. 1 and 7.) The formation of these rings depends on the 

 rapidity with which the fungus grows. The most perfect rings of 

 pustules are formed when the fungus grows most rapidly. (Pis. I and 

 II.) Cold weather will be followed by a more or less irregular devel- 

 opment of the pustules. (PL IY, fig. 3.) They then break through the 

 epidermis at many points, as shown on PL IY, figs. 3 and 7. The 

 arrangement of the fruiting bodies in rings is a conmion phenomenon 

 among fungi. Where a single spore germinates in a medium where 

 the food supply is abundant on all sides, the hypha? generally grow in 

 all directions with equal rapidity. When the period for the develop- 

 ment of spores has arrived, the spores will be formed from hyphse of 

 the same age, i. e., at points equally distant from the original point of 

 infection. The phenomenon of fairy rings is a notable instance among 

 the higher fungi. Alternate periods of low and higher temperature 

 may account for the intermittent development of fruiting bodies, and 

 hence the formation of successive rings. 



The pinkish appearance of diseased fruit is due to the spore masses 

 which exude from the pustules. After a rainstorm the interior of the 

 pustules looks sooty black and the mouths ragged, all the spores 

 having been washed off. 



