424 Brooks: The Fruit Spot of apples 



sterile form of Fusicladium dendriticum, thus making the " Stip- 

 pen der Aepfel " identical with scab. 



Wortmann (5) made extensive studies of the " Stippen der 

 Aepfel." He described the disease as producing numerous brown 

 spots on the surface of the fruit. At first these were but 1 to 5 

 mm. in diameter and entirely separate and distinct, but later they 

 might become larger and more numerous, practically covering 

 the entire surface of the apple. The spots usually developed 

 after the fruit had been gathered and while it was passing through 

 its final ripening processes, but with especially susceptible varie- 

 ties they sometimes appeared while the apples were still on the tree. 

 The tissue beneath these spots was browned, possessed an over- 

 abundance of starch and in late stages was bitter to the taste. 

 He did not consider the disease to be of fungous origin, not only 

 because he was unable to find any trace of mycelium in the 

 affected tissue but also from the fact that the spots were often 

 covered by a smooth and unbroken epidermis and might be found 

 at a depth of one centimeter from the surface and entirely sepa- 

 rated from all other affected tissue. He believed that the disease 

 was a physiological one and that conditions of transpiration were 

 largely responsible for its occurrence. He found that varieties 

 apples that were susceptible to spotting had more lenticels and a 

 thinner-walled epidermis than those less affected by the disease. 

 On the other hand, these same susceptible varieties gave off less 

 water in transpiration than the more resistant ones. From tnes 

 observations and from the previously known fact that spot ing 

 might be prevented by a rapid drying of the fruit, he drew t e 

 conclusion that the extent of the disease was not determined y 

 the actual amount of transpiration but by the readiness with 

 which water was conducted from deeply seated cells to rep a 

 that lost in transpiration. The varieties that had the slowest rate 

 of conduction were the ones that were most seriously a ec 

 The concentration of the cell sap in the exposed tissue was 

 real cause of the injury and the acids and acid salts were 

 active agents in killing the cells. As an explanation oi the ac^ 

 that apples do not become spotted when dried very rapid y, 

 suggested that under such conditions the acid did not have 1 

 to act. He believed that the nature of the substances in the c 



