44 PEACH YELLOWS. 



(2) It may be conveyed by seemingly healthy buds when these are 

 taken from diseased trees. This is proved by Experiments 2 and 5. 



(3) Only a very small amount of infective material is necessary, pro- 

 vided it be in the forms of living cells, which can be induced to unite 

 with the actively growing tissues of the tree. 



(4) The disease has a longer period of incubation than we have been 

 accustomed to suppose. (See Experiment 2, especially Table i, columns 

 5 and 6, and plate xvm, Fig. 1. See also the Excisions, especially 

 B 16, 18; E 3; G 3, 4, 5, 6, 12, 19; and the note under G 3.) 



(5) The death of the entire tree occurs, ordinarily, only after a very 

 considerable period, i. e., several years. 



HYPOTHESES RENDERED PROBABLE. 



(1) The whole tree is affected when symptoms appear in any part of 

 it. This inference rests upon Experiment 2 ; a small part of Experi- 

 ments 4 (?) and 5 ; and almost all of the excisions, 52 in number. It is 

 hoped that experiments now underway will settle this point definitely. 



(2) In some cases, perhaps in many, the period of incubation, i. e. 9 

 the time between the insertion of a diseased bud and the appearance of 

 the disease, is longer than any yet clearly established. This is sug- 

 gested by many things, especially by the behavior of some of the Bar- 

 nard trees (Experiment 4); by the Excisions E 3, G 3, and the Wilson 

 tree ; and by Professor Goff's tree. 



(3) The disease is also communicated to budded trees in some other 

 way than by bud inoculation. This is probable in case of many young 

 trees, and is almost certain in case of old trees. In some of my ex- 

 periments the period of incubation was very considerable, and this 

 is one of the striking peculiarities of yellows, but it is too brief to 

 account for the appearance of the disease after the second or third 

 year, except possibly in case of some of the trees budded at Colonel 

 Barnard's. The evidence in favor of outside infection becomes stronger 

 in proportion as a tree gets older. Of course, it goes without saying 

 that additional experiments may demonstrate the period of incubation 

 in some cases, and perhaps in many, to be much longer than any yet 

 established. 



(4) The trees are not infected through the blossoms. This is inferred 

 from the result of the excisions, and from the fact that, in some cases, 

 the disease appears to develop between fall and spring, and to stimu- 

 late the blossoms themselves to an unnaturally early development. 

 About fifty cases of this kind came under observation during the very 

 mild winter of 1889-'90, and many additional ones in the spring of 

 1891. 



(5) Since diseased trees have been shown to be very full of infectious 

 matter it must be that for unknown reasons much of this fails to find 

 an immediate entrance into healthy trees. Otherwise the peach would 

 soon disappear entirely. 



