296 STATE HORTICULTURAL SOCIETY. 



them develop yellows this fact may he recorded aud given its due weight in 

 estimating liual results. If these trees from which the scions were taken re- 

 main healthy, while those budded on the ])lum stocks contract yellows, then 

 underground parasites are excluded, and, if yellows is a parasitic disease at 

 all, the cause must act through the parts above ground. Such a result would 

 also show that the insertion of diseased buds is not a necessary factor in the 

 production of yellows. 



From the fact that the disease first appears in the fruit, and occasionally 

 only in one or two })eaches, it has been thought that yellows might be due in 

 some way to diseased pollen or to bacteria which find an entrance through 

 the moist unprotected stigma. On this theory the contagium is supposed to 

 enter the tree in the spring of the same year that the disease appears. If this 

 is so, one ought to be able to cut out the disease, at least in some instances. 

 Practically, the cells and vessels of the living parts of the tree are all closed 

 cavities; i. e., there are no capillary tubes large enough and at the same time 

 long enough to easily permit the passage of micro-oigauisms from one part of 

 the tree to another, if, indeed, there are any bacteria small enough to pass at 

 all in this way without destruction of the tissues. On such a theory it must 

 therefore take considerable time for a germ to penetrate to all parts of the 

 tree, since there is no breaking down and decay of tissues such as occurs in 

 pear blight and other plant diseases known to be due to bacteria. The only 

 destruction of tissues I have observed was due to "guuimosis." In the wood 

 of diseased shoots I have found closed gum-cavities, due to the metamorpho- 

 sis of fibers and vessels, but I do not yet know how constant a symptom this 

 may be, or just what relation it may bear to the disease. Gammosis is known 

 to occur in plums and cherries, which are not subject to yellows. 



The almost universal statement of the books is that yellows can not be cut 

 out of a tree, no matter how slightly affected. At first I was disposed to ac- 

 cept this statement as true beyond question; but having heard counter state- 

 ments, and having seen in Delaware one perfectly healthy tree from which 

 the disease is said to have been removed three years ago by a severe excision, 

 aud having seen in another orchard some indication of recovery after similar 

 excisions, I determined to repeat this experiment. Two trees were selected 

 in orchard No. 12, eighteen in orchard No. 14, and three in the orchard from 

 which Photo. X was taken, that tree, however, not being one of the three. 

 The excisions were made in September, 1887, with the utmost care. The 

 trees were all young and vigorous, aud were only slightly diseased; i.e., 

 they bore premature peaches on one limb only, or on a few small branches, 

 the rest of the tree bearing healthy peaches aud full grown dark green foliage. 

 In most cases the diseased limbs also bore spring foliage of normal size and 

 color, and had not yet sent out many of the characteristic shoots; in some in- 

 stances not any. In every case I removed not only the diseased branches, but 

 also the large sound limbs which bore the affected parts, taking away from 

 one-third to one-half the tree. These trees Avere previously selected with great 

 care, as being those in which such an experiment was most likely to succeed. 

 After the excisions each one was again carefully scrutinized in all parts, so 

 that by no possibility should any portion be left which bore external mani- 

 festations of the disease. I did not use a disinfected saw, but the stumps 

 Were carefully painted with red lead, an 1 this was rubbed in, especially in 

 the vicinity of the cambium. 



In August, 1888, these trees were re-axamined. All of them bore prema- 



