52 MISCELLANEOUS PAPERS. 



Again, on August 21, 1907, this same fungus was used for inocula- 

 tions, which were made in the evening just after a heavy rain. For 

 the next two days the sky was overcast and occasional showers fell. 



The results of these three sets of inoculations with Coniothyrium 

 were negative. Spots were found here and there on the inoculated 

 leaves, but no more than on the checks which were sprayed with 

 sterile water. Similar spots, never more than two to a leaf, were 

 found throughout the nursery at this time and were evidently pro- 

 duced by a natural infection with Sphaeropsis. 



CONCLUSIONS. 



The following conclusions may be drawn from the results of the 

 inoculation experiments described in the preceding pages : 



Sphaeropsis malorum Pk., the black-rot fungus, is parasitic on 

 apple leaves, producing circular (or irregular) reddish brown spots 

 an eighth of an inch or more in diameter, and is undoubtedly the 

 cause of the apple leaf -spot disease which occurs in the middle West. 

 The common apple leaf-spot disease of the Eastern States, being so 

 similar in every respect, is doubtless caused by the same fungus, 

 although some other fungi may possibly produce similar spots. 



Coniothyrium pirina (Sacc.) Sheldon, although it occurs abun- 

 dantly on apple leaf-spots, appears to have nothing to do with their 

 formation. 



The several other fungi that were tested, such as Hendersonia sp., 

 Coryneum sp., Pestalozzia sp., and Altemaria sp., proved to be non- 

 parasitic in these experiments and probably occur on leaf spots only 

 as saprophytes. 



SOURCE OF INFECTION. 



/Sphaeropsis malorum is perhaps the most common fungus that 

 inhabits pome-fruit orchards east of the Rocky Mountains. It is the 

 cause of the black-rot of the apple, the pear, and the quince and pro- 

 duces cankers on trunks and branches of these fruit trees. It occurs 

 abundantly on dead twigs and branches in nearly every orchard, pro- 

 ducing spores in enormous numbers. This is perhaps the most fertile 

 source of infection for both fruit and foliage. In old orchards, par- 

 ticularly where pruning is neglected, the leaf-spot disease is much 

 worse than in young orchards. The leaves of young trees adjacent 

 to an old orchard become more spotted with the disease than those 

 farther removed. Another source of infection is the diseased fruits 

 of the previous year's crop. Although the fungus fruits only spar- 

 ingly on leaves on the tree, it produces fertile pycnidia in consider- 

 able numbers on these leaves after they have' fallen to the ground. 



121— v 



