280 STATE HORTICULTURAL SOCIETY. 



Orchard Xo. 1, however, has received no manure, (excei^t two loads on one 

 spot. Moreover, in uninfected localities, I have seen orchards which have 

 been heavily manured, and they were healthy. The general tendency of 

 nitrogenous manures is toward the excessive production of wood and foliage. 



Summing up the evidence, I am inclined to think that, in infected dis- 

 tricts, nitrogenous manures have a bad influence, but to what this is due I 

 am unable to say. 



DEGENERACY DUE TO CONTINUED PROPAGATION BY BUDDING. 



A sufficient answer to this is the statement that yellows affects seedling 

 trees no Ifss destructively than budded ones. This I have verified repeat- 

 edly. Seedlings are not exempt, and I have not been able to show that our 

 oldest varieties are any more subject to this disease than those but recently 

 originated. My examinations in over two hundred orchards have led to no 

 positive result. All varieties appear to be subject in like degree when all 

 other conditions are the same. In some orchards, indeed, certain varieties 

 were much worse affected than others; but often the very next orchard would 

 furnish contradictory evidence — e. g., in No. 1 of this report, Christiana was 

 most badly diseased, while in No. 4 this variety had suffered very little. In 

 No. 2, Mountain Eose is badly diseased; in Nos. 4 and 5, this variety is 

 scarce ly at all affected. In No. 5, Early Kivers suffered much in 1887 and 

 previous years; in No. 12, not at all until 1888. 



Even in the same orchard other things than variety control the spread of 

 the disease. This is quite different from what occurs in many diseases due to 

 fungi, where the limiting effect of variety is very sharply marked. In peach 

 yellows, no matter which variety is first diseased, all become affected alike 

 in the course of a few years. Neither is it true, as some have asserted, that 

 the variety which shows the disease first is always the first to become badly 

 affected. In orchard No. 5 yellows first appeared, in 1885, in one tree in the 

 Mountain Rose variety. This was removed in the fall, and no more affected 

 trees appeared in that variety until 1888 — then only three. Other varieties, 

 however, were affected in 1886 and 1887, some quite badly. 



Knight, Von Thilmen, and some other European writers have insisted that 

 continued propagation by buds, cuttings, etc., leads to degeneracy, and there 

 is a very general impression among farmers aud fruit grower that varieties 

 "run out." This theory is not wholly unreasonable, and yet a vast amount 

 of careful experimenting must be done before it can be said to rest on any 

 broad basis of well-established facts. Propagation by budding secures the 

 continuation of a variety for an indefinite period, but this is tha ordinary 

 method of reproduction in some of the lower plants, and is something quite 

 different from inl^reeding. We know by direct experiment that the latter is 

 injurious, but our knowledge of the effect of continued budding propagation 

 is largely guess work. It may produce deterioration, but there is no unim- 

 peachable evidence that it does. In the higher animals there is a distinct 

 individuality, but in some of the lower auimaisand in plants it is difficult to 

 decide what constitutes an individual. Strictly speaking, we cannot take an 

 anology from the animal world and say that budding perpetuates an individ- 

 ual indefinitely, and must therefore lead to superannuation. If we are to use 

 this term at all, it would probably be best to restrict it to each new- formed 

 bud, in which case there certainly could be no such thing as superannuation. 



