182 AMERICAN POMOLOGY. 



are deleterious in their impressions on the animal system. 

 Even the palatable mushroom is always poisonous to some 

 persons, and may become so to all under certain circum- 

 stances. It is equally evident that fungi frequently oc- 

 casion diseases in the vegetable kingdom. The smut of 

 wheat and maize, the rust of wheat, ergot of rye and 

 grass-seeds, and specks, cracks, and discoloration of the 

 skin of the apple and pear are of this nature. 



"The microscopical examinations of Prof. Salisbury and 

 others have detected the presence of certain species, in- 

 festing extensively pear trees about the period of attack 

 by the blight* They have made similar discoveries that 

 lead to the conclusion that the curl of the peach leaf, 

 the potato disease, and the blight of pear trees, all have 

 their origin from the cause assigned in my second prop- 

 osition. 



"Under this head still another disease of our fruit 

 should be noticed. I have watched carefully the sudden 

 and premature decay of our plum crop, at the period of 

 its ripening, for the last fifteen years. From hints afford- 

 ed by the work of Prof. Mitchell, and several microscopic 

 observations of my own, I was induced to publish an ar- 

 ticle in ' The Florist,' of Philadelphia, in the year 1855, in 

 which I imputed the origin of the disease to the Torula 

 or some analagous species of parasitic fungi. The disease 

 still prevails among us, and it is sure to destroy all the 

 plums which escape puncture by the curculio. It is, how- 

 ever, generally overlooked by pomologists, and its effects 

 are charged to the depredations of that insect. Similar 

 disease occasionally impairs our peach and apple crops, to 

 a less extent. Whenever it occurs on either of these va- 



