PEACH YELLOWS. 259 



is capable of maintaining itself to a considerable extent outside of cultivation, 

 in fence rows, hedges and other neglected places. In the more favored parts 

 of this country the peach fulfills all these conditions, and has done so for 

 more than two centuries. In my examinations on the Deleware and Chesa- 

 peake peninsula in 1887 and 1888 I saw at least fifty orchards of ages ranging 

 from twenty to thirty years, and I saw a few still older. Such orchards are 

 by no means infrequent, except where yellows has prevailed for a long time. 

 Even in the relatively severe climate of Michigan orchards have lived 

 twenty-five and thirty years. The average age of the orchards in Maryland 

 and Delaware is only about sixteen years, but this is to be attributed to over- 

 production and neglect rather than to climate. If our trees were pruned as 

 carefully as European trees they would undoubtedly live as long. Even with- 

 out special care they sometimes reach a great age. There are well authenti- 

 cated cases on the Atlantic coast of peach trees which have lived forty or even 

 fifty years, and George Thurbur mentions one in Virginia which reached the 

 age of seventy years. 



That Chinese peaches are more hardy than our own is a belief rather than 

 a well established far>t. They are certainly inferior in flavor and probably 

 not hardier than the commonly cultivated *' Persian " sorts. I have myself 

 this year seen well marked yellows in North China peaches growing in Dela- 

 ware, and have no doubt that Chinese peaches will prove subject to all the 

 diseases incident to other races, and on a -priori grounds, in the -ibsence of 

 sufficient well-authenticated information, I have no doubt that in China itself 

 they are subject to various diseases, especially where grown in quantity. 

 Certain, at least, is the fact that in the North Island of New Zealand the 

 peach has been nearly exterminated within the last ten years by some myste- 

 rious blight. 



Nevertheless, with some show of reason, peach yellows has been attributed 

 to various unfavorable climatic conditions. The relation of these conditions 

 to yellows will, therefore, be dicussed in the following pages. Four theories 

 have received most frequent mention by writers on this subject, and as no 

 proofs or valid arguments have been advanced in favor of any others it will 

 be sufficient to restrict attention to these four, with a view to determine, if 

 possible, just what relation these supposed causes bear to the disease. 



The theory of general change in climatic conditions may be dismissed with 

 a word or two. It is easy to propound and difficult to establish. In refer- 

 ence thereto it may be said : (1) There is no evidence of any marked change 

 in the climate of the United State during the last one hundred years ; and 

 (2) if there were, there is no evidence that the outbreaks of peach yellows have 

 conformed to any such change. We may, therefore, set aside this theory 

 until evidence is adduced in proof of both propositions. 



The theory of early autumn frosts has been urged with more show of rea- 

 son. When we reflect upon the function of the leaves, and on the nice 

 balance between roots and foliage which is necessary for the health of a grow- 

 ing tree, it is evident that any premature destruction of the foliage must not 

 only affect the maturing wood, but also more or less seriously injure the 

 whole plant. With this fact in mind, I have given careful attention to the 

 subject, the more because some very considerable authorities in horticulture 

 have favored this theory, and have stated by way of proof that this disease 

 never occurs in the South or when the peach is grown under glass. 



After careful inquiry my conclusion is that early frosts have nothing what- 



