20 THE BITTEK EOT OF APPLES. 



same time it is probable that a large percentage of the infections in 

 an orchard start in fruits which have been wounded in some way, gen- 

 erally by insects. When one reflects that the number of spores which 

 fall on a fruit is generally very large, it is strange that there should 

 be onh T very few infections or sometimes only one infection. This 

 point is one which will require additional careful study. 



After the first hypha has entered the tissue below the epidermis it 

 branches rapidly. The hypha? grow in the intercellular spaces, absorb- 

 ing the sugar and other products from the apple cells. (See PL V, fig. 

 3.) The affected cells turn brown and separate, and after a time they 

 collapse. It is then that the presence of the fungus becomes noticeable 

 on the outside in the form of the brown, sunken spots mentioned above 

 (PI. IV. figs. 1 and 2). The fungus hypha? grow in all directions from 

 the original point of infection with great regularity. As they extend 

 outward the cell groups attacked become brown in turn and collapse 

 more or less. This regular development gives the affected mass of 

 cells the circular form visible on the outside. 



Early in the season the brown areas are about one-half of an inch in 

 diameter before there is any evidence of spore formation; later on, 

 during the height of an epidemic, the spores 'begin to form when the 

 affected areas are still very small. The spore-forming stage is evi- 

 denced by the appearance of numerous small raised points, which push 

 up the epidermis in a brown spot at irregular intervals. These points 

 are composed of masses of parallel hypha? which grow outward from 

 the cells just underlying the epidermis. These hypha? are short and 

 so arranged as to form a low cone, whose apex pushes against the 

 epidermis as the hypha? composing it grow in length. These hypha? 

 are at first colorless and then turn olive colored. Ultimately, either 

 by pressure or because of the solvent action of an enzyme, the tip of 

 this cone breaks through the epidermis. On the outside the tips of 

 the cones appear as small dark specks. The unicellular spores are 

 formed by abstrictiou from the ends of the hypha? composing the 

 cone, many spores being formed from each hypha. Great masses 

 of these spores issue from the hole made in the epidermis and 

 remain on the outside as bright pinkish, glistening masses, adhering 

 to the tips of the cones. The latter are the pustules or sori. When 

 the fungus is growing rapidly the pustules or sori may form when the 

 spots are but one-fourth of an inch in diameter. The spore masses 

 are sticky and adhere firmly to the mouth of the pustules. Some- 

 times, especially during nights when a heavy dew has fallen and there 

 is an abundance of moisture in the air, the spores will be discharged 

 forcibly in the form of tendril-like masses. (PI. VI, fig. 2.) 



As stated above, the sori appear in irregular groups early in the 

 season. Later in the summer, when the fungus is growing rapidly, 

 they break through the epidermis in groups, forming very regular 

 rings (PI. I). These rings are striking objects shortly after the dis- 



