FlOR11\-\ and CaIIIOIINIA LAlK)RAT(MUliS 239 



understand " why thousands of vines of the most susceptible of 

 all the varieties, the old Mission, should prosper for a century 

 over all this vast region, mk\ why at present perfectly healthy 

 cuttings set out [there] grew with perfect health for one or 

 two years and then [contracted] this disease in all its strong 

 characteristics." 



Like Smith in peach yellows, while he suspected a parasite, 

 cellular examinations made with the most advanced learning in 

 section cutting, staining, indeed, working up some new methods 

 of his own in studying the " living plasmodium," still failed to 

 establish any orj^anism positively proven to be the cause of the 

 disease. In his monograph, "Additional Evidence on the Com- 

 municability of Peach' Yellows and Peach Rosette," '' Smith had 

 spoken of a " germ or virus of some sort " transmitted from 

 diseased to healthy parts of a tree. This was a conclusion as to 

 peach rosette. As to peach yellows he had concluded, "Only a 

 very small amount of infective material is necessary, provided it 

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

 actively growing tissues of the tree." The problem of how the 

 infectious matter makes its entrance into healthy trees was still 

 unsettled, as were the disease's incubation period, the exact nature 

 of the contagium, and its method of spread other than by bud 

 inoculation.'"" Late in the year 1893, Smith, thanking F. H. Harper 

 of Still Pond, Maryland, for another prescription and claimed cure 

 for peach yellows, expressed the opinion that the disease, " not 

 being due to a root aphis, or, so far as I can make out, to any root 

 parasite," seemed best explained as " a something in all the juices 

 and tissues of the diseased tree, as shown very clearly by bud 

 inoculations." This was not his final writing upon the subject. 

 He had observed the seemingly varying degrees of resistance 

 shown by various trees and had not been unmindful of the pos- 

 sibilities of searching out the bearing which immunity might play. 

 But he had decided to put his " time on lines of work which 

 seem[ed] to promise better results." 



On March 27, 1893, Acting Regent Thomas J. Burrill of the 

 University of Illinois had advised Smith that the large peach trees 



"Bulletin 1: 54, U. S. Dcp't of Apric, Div. of Veg. Path., Washington, Gov't 

 Print. Office, 1891. 

 '" Idem, 44-45. 



