PEACH YELLOWS. 251 



I should expect to find these symptoms correlated with peculiarities of 

 microscopic structure, some of which might perhaps prove of diagnostic 

 value, but up to this time I have not been able to make the necessary num- 

 ber of careful observations. What induces this prolonged activity of the 

 cambium remains to be determined. lb is apparently something in the 

 nature of an irritant. 



Other abnormal appearances, e. g., the black heart wood, mentioned as 

 symptomatic by various observers, and the cracked and discolored bark found 

 by Professor Penhallow, were objects of diligent search and were observed 

 occasionally. However, not having found these two symptoms constant in 

 yellows infected trees, and having found the same in many trees not diseased 

 by yellows, and even in localities where yellows has never appeared, I am 

 constrained to rule them out as not peculiar to this disease. I think peach 

 s ems are apt to become black hearted by severe freezing or from very slight 

 injuries, if at all exposed to the weather. The appearance of the bark on trunks 

 and main limbs was noted with great care in hundreds of trees, diseased and 

 healthy. In the early stages of the disease in almost all the younger trees, i. e., 

 those under six years of age, the outer bark was smooth and fair. In older 

 trees the bark is naturally more or less rough and cracked. I could find 

 nothing in color or cracking of the bark which appeared to me to be of diag- 

 nostic value, although in some cases, on shoots of but a few years' growth, 

 the production of cork in irregular patches appeared to be excessive. VV hether 

 this is a peculiarity of any importance remains to be determined. 



Since, in spite of all that has been said and written on the subject, there 

 is still much confusion in the minds of peach growers as to exactly what con- 

 stitutes yellows, I have thrown my couception of it into the following propo- 

 sitions, the symptoms being noted in order of appearance : 



DIGEST OF SYMPTOMS. 



(1) Prematurely ripe, red spotted fruit. 



(2) Development upon the trunk and branches, which bear, or have borne, 

 the diseased peaches of secondary or summer shoots, often in great numbers, 

 and always dwarfed and feeble in appearance. 



(3; A very marked tendency of the buds on these secondary shoots to 

 develop the same season, forming sometimes in this way within a few months 

 secondary, tertiary, quartan and quintan branches. 



(4) The appearance of the disease the next spring in the entire growth of 

 the tree, or at least of the diseased parts — the shoot-axes being shortened and 

 the foliage dwarfed and sickly, of a yellowish or reddish-brown color, and 

 with a greater or less tendency to curl from end to end, and to roll sidewise, 

 so that the lower surface becomes the convex outer surface. Sometimes, how- 

 ever, the disease affects the terminal shoots the same autumn, causing the 

 winter buds to develop either before or after the leaves have fallen. 



(5) A slow progress of the disease from limb to limb, so that in one or two 

 years, or at most three years, the whole tree is involved. 



(G) Co-ordinate with the progress of the disease from part to part, a 

 marked diminution of the vitality of the tree, ending in death. 



These are symptoms characteristic of peach yellows, and they seem to me 

 quite as definite as those of any specific disease. If peach yellows, as I have 

 seen it and have defined it, is not a specific disease, due to some constant 

 cause or causes, then neither is glanders or anthrax, or measles or small-pox. 



