I20 NATURAL HISTORY BULLETIN. 



It has been decided that the original supposed determina- 

 tion of this species must have been erroneous. The cHseased 

 leaves show no evidence of the presence of a fungus. 



During this series of investigations the usual laboratory 

 methods have been followed. For the dissolution of the cell- 

 walls of the host and certain inter-cellular substances a satu- 

 rated solution of chloral hydrate or potash was used. The 

 differentiation of the mycelial tiireads of the fungus was 

 then readily accomplished by the aid of some suitable stain; 

 an aqueous solution of eosin giving very satisfactory results. 



In conclusion, I wish to express to Mr. A. B. Seymour my 

 very sincere thanks for his most generous treatment in regard 

 to material and literature. I also wish to acknowledge my in- 

 debtedness for material to Dr. H. W. Harkness, Prof. L. H. 

 Pammel, Prof. B. D. Halsted, Dr. J. J. Davis, and Mr. F. C. 

 Stewart. Prof. Wm. Trelease sent me the entire collection of 

 the Missouri Botanical Garden for examination; and Mr. B. 

 T, Galloway granted me the same privilege with the collec- 

 tion of the Agricultural Department at Washington. These 

 herbaria are especially rich in foreign forms, and by this exami- 

 nation I was enabled to become familiar with a large majority 

 of all Exoascea?, an enumeration of which would not come 

 within the scope of this paper. 



Cambridge, yuiir, 18^4. 



It may be advisable to give a list of the fungus species, with 

 their American hosts: 



ExoASCUS PRUNI Fuck, defoi-ming tlie fruit of — 

 Priiniis domcsf'ica Linn., Common rium. 

 P. virginiana Linn., Choke Cherry. 

 P. fadiis var. aiiicricana is probably a synonym of P. vtrghiiana. 



ExoAscu.s coMMUNi.s Sadch. deforming the fruit of — 

 Pniniis amcricana Marsh., Common Wild Plum. 

 P. iiiarituua Wang., Beach Plum. 

 P.pKinila Linn., Dwarf or Sand Cherry. 

 P. nigra Ait. 



P. subcordata, Pacific Wild Plum. 

 De Soto Plum, a variety of P. cancrkana found wild in Wisconsin. 



