244 STATE HORTICULTURAL SOCIETY. 



CHARACTERLSTICS OF PEACH YELLOWS. 



In the preceding pages, while dealing with the history and distribution of 

 peach yellows, I have assumed it to be a specific disease. Is it really so, or 

 is it only a sort of a marasmus, due to various causes and itself as variable as 

 the conditions which produce it? In other words, is the name yellows a 

 misnomer and the disease a nonentity, as some would have us believe, or 

 is there a well defined set of svmptoms to which this term may properly 

 apply? 



By the term specific we mean ordinarily a disease which runs a definite 

 course and is characterized by a more or less peculiar set of symptoms, clear- 

 ly distinguishing it from other maladies. Whether we know much, little, or 

 nothing of the cause of a specific disease, of one thing we are never in doubt : 

 it begins, progresses, and ends in a definite way; it can be defined; it is a 

 genuine disease. Although in different individuals therfe may be peculiari- 

 ties due to idiosyncrasy or to unknown causes, yet in its broad, essential 

 features the disease is the same in all individuals, so that from the careful 

 study of a few typical cases we can readily predict what will be the general 

 course of the disease in any number of other cases. Instances of such 

 diseases readily occur to all, e. g., in man, consumption, small-pox, diph- 

 theria ; in the lower animals, anthrax, glanders, swine plague ; in plants, 

 smuts, rusts, mildews. Each of these diseases is characterized by a very 

 definite set of symptoms, so that we are in no great danger of mistaking 

 one for another. 



Unquestionably by the term yellows much confusion has arisen, different 

 persons having used it to convey different ideas. By this expression some have 

 meant simply the results of starvation, or the effect of very wet subsoils ; 

 others, no doubt, have had in mind that stunting peculiar to trees infested 

 by root-aphides ; others again, the effects of the peach-tree borer. By the 

 term yellows I mean none of these things, though any one of them may 

 cause the foilage to become yellow, and though any or all of them may be 

 found in the tree along with genuine yellows, just as a person may at the 

 same time have measles and whooping-cough, scarlet fever and diphtheria, 

 or consumption and ague. 



Peach yellows as it occurs in Michigan, and as I saw it in hundreds of 

 trees in many orchards in Maryland and Delaware in 1887 and 1888 is a 

 disease of haste and waste; the fruit ripens too soon; the buds push too 

 soon ; assimilation is disturbed ; the stored starch and other food materials are 

 wasted by excessive and unnatural growth; and the entire vitality of the tree 

 is exhausted in the course of two or three seasons. 



Healthy peaches giow somewhat slowly until a few days before the time of 

 their maturity; then they increiise in size rapidly, and all ripen at about the 

 same time, this time varying with the latitude, but being quite constant for 

 the same variety in any given locality. Upon the variability of different 

 varieties, as to time of ripeniug and the constancy of the same variety, 

 depends the peach season and the whole peach industry. For example, in 

 middle latitudes of the eastern United States the peach grower knows to a 

 certainty that he may expect the Early Louise or Early Rivers to be ripe at 

 a given date in July; the Mountain Rose and Crawford's Early at two given 

 dates in August; the Old Mixon, Stump, Crawford's Late, Smock, Bilyeu's, 

 etc., at successively later dates. Oousefjueutly, in planting his orchards he 



