50 MISCELLANEOUS PAPERS. 



transferred to slanted apple or potato agar. The writers separately 

 made many sets of cultures by this method, using spots from leaves 

 of Ben Davis. Winesap, and White Pearmain trees. Within 

 a few days by the aid of a hand lens liyphae could be seen growing- 

 out from the center or margins of the small spots. Mycelium devel- 

 oped rapidly and in about two weeks spores were formed, so that 

 the fungi could be identified. The results were uniformly the same. 

 In all cases in which the youngest spots, that is, those one-sixteenth 

 of an inch or less in diameter, were used, the fungous growth was a 

 pure culture of Sphaeropsis malorum Pk. In cultures made from 

 the older sj)ots, in which the central tissue had become brown, some- 

 times a pure Sphaeropsis was obtained, but more often a mixture of 

 things. Goniothyrium pirina developed about as commonly as 

 Sphaeropsis, both species often growing from the same spot. In 

 addition to these two fungi, two species of Alternaria, a Claclospo- 

 rium, bacteria, and yeasts were frequently present. 



This cultural work, frequently repeated, gave evidence that Sphae- 

 ropsis malorum, always developing from the youngest spots, was the 

 specific cause of the disease and that the other organisms were mere 

 concomitants. Of course, to prove this inoculation experiments were 

 necessary. These were made as soon as pure fruiting cultures of the 

 different fungi were obtained. 



INOCULATION EXPERIMENTS. 



A number of different sets of inoculations were made, but the 

 method of procedure was the same in each case. With a sterile 

 needle the fruiting fungus was scraped from the surface of the agar 

 and transferred to a tube of sterile water. In cases where pycnidia 

 were present these were crushed against the side of the tube with a 

 sterile glass rod to set free the spores. In order to ascertain the 

 jD'resence of mature spores a hanging drop of the fluid was always 

 examined microscopically. This spore-bearing liquid was then 

 sprayed on both surfaces of clean young leaves with an atomizer. 

 Trees in more or less isolated young orchards were selected, and no 

 two fungi were used on the same tree. From 20 to 40 leaves on two 

 or three different shoots were involved in each inoculation. Checks 

 were always made on separate trees by spraying 10 or 50 leaves with 

 sterile water. 



The first inoculations were made on May 28, 1907. The fungi 

 used were Sphaeropsis malorum, and the undetermined species of 

 Coryneum, Hendersonia. and Alternaria previously mentioned. It 

 was raining at the time and the weather continued wet for several 

 days. 



121— v 



