THE NICHOLSON TREES. 



21 



Up to date only one case of yellows has developed in the imbudded 

 trees, the tree noted as suspicious in 1889. 



A number of the unbudded trees at one end of the orchard died in the 

 spring of 1890 from some unknown cause, not yellows. They dried up 

 suddenly, much as if they had been injured by plowing or by moles. 

 The roots, however, seemed intact and the origin of the trouble was not 

 to be learned in July. It is sufficient that it was not yellows or any- 

 thing suggestive of that disease. Four of the trees set on sod ground 

 also dried up during the summer. All the rest of these trees (86) made 

 an excellent growth in 1890 and were thrifty and beautiful to look upon 

 (plates xxin and xxiv).* The photographs from the unbudded trees 

 represent average specimens, while those from the inoculated trees in- 

 clude the best, and, in fact, almost everything. 



For several reasons this experiment is more interesting than No. 1, 

 although the results are identical. First, the inserted buds were taken 

 from shoots that appeared to be healthy ; second, the disease developed 

 more slowly than in Experiment 1, owing probably to the different char- 

 acter of the buds ; third, a smaller amount of infective material was 

 used ; fourth, the inception and progress of the disease occurred in a 

 locality entirely free from yellows. This experiment confirms No, 1. 

 In addition, it proves that yellows may be communicated by parts of a 

 tree which seem to be healthy and renders it probable that the disease 

 is incubating in all parts of a tree when it appears in any part. In 

 passing, it may be said that the results of the excision experiments de- 

 scribed in Part III point to the same conclusion. It is also noteworthy 

 that each of these trees was infected by a single bud, and that all of 

 these buds were cut from a single tree. The inference is very strong 

 that this one tree contained infective material sufficient to destroy en- 

 tire orchards if properly introduced into the trees. Both experiments 

 go to show that the germ or virus of the disease must be quite uni- 

 formly distributed through the affected parts. 



Experiments 3 and 4 (the E. (r. Nicholson trees and the D.P. Barnard 

 trees) are incomplete, owing to the temporary discontinuance of this 

 investigation in the spring of 1888. 



* These trees were re-examined August 12, 1891, with the following results: 

 Average height of the north two rows (37 trees), 9.9 feet; average circumference 

 of trunk, 8 inches. Average height of the south three rows (49 trees), 8.1 feet; aver- 

 age circumference of trunk, 5.7 inches. Twelve of the trees have mildewed badly 

 this year, one has yellows, and several others are small. Otherwise all are healthy 

 and growing vigorously. The difference in amount of growth is referable to the un- 

 like methods of treatment. They have been cultivated with crops as follows: 



The growth of a crop of wheat in 1889 and the absence of cultivation the follow- 

 ing year, when the trees were in clover sod, checked the growth of the south three 

 rows nearly one-third. Of the inoculated trees only six remain, and they are like the 

 three left from Experiment 1. 



