Bacteria in their Relation to Vegetable Tissue. 21 



lated with B. amylovor us, sub-epidermally, on March 3. March 12, 

 the blight was well marked as a blackened patch for nearly an inch 

 on each side of point of inoculation. Period of incubation, therefore, 

 9 days. 



Set 2. Two 2-year old' trees, of blight-proof variety, budded 

 on Japan stock, were inoculated, sub-epidermally, March 17. Evi- 

 dence of blighting in leaves and stems readily recognizable on 

 March 25. Incubation period, 8 days. 



Set 3. 2-year old budded Clapp's Favorite (a variety readily sus- 

 ceptible to the disease in the orchard) was inoculated in the same 

 manner, March 3. March 12, diseased condition apparent, although 

 not as well marked as in Set 1. Period of incubation, 9 days. 



From this set of experiments, it will be noted that those varieties 

 (Sets 1 and 2) which under natural conditions are known to be much 

 more refractory than others (3), not only lost their partial natural 

 immunity when subjected to artificial inoculation, but yielded to the 

 disease fully as quickly as did the variety that was naturally sus- 

 ceptible. This artificial inoculation is, however, a much severer test 

 than they receive under the operation of ordinary conditions of 

 cultivation, but it shows that the varying degrees of susceptibility, or, 

 in other words, immunity can be overcome under certain conditions. 



Waite attempted to infect two different species of Cratsegus (C. 

 oxyacantha and C. tomentosa, var. parviflora) by atomizing the 

 flowers, but found that only the latter succumbed to the action of the 

 germ. Here again is a case of immunity where one variety is exempt, 

 under certain conditions, from the disease. The immunity in this 

 case is, however, not a deep-seated condition, as is shown by the suc- 

 cessful infection of the latter variety by puncture inoculation, where 

 the bacteria were actually introduced into the tissues. Other species 

 of the pomaceous group of the Rosacese are more or less susceptible 

 to the disease, although much less so than the pear and apple. The 

 cultivated species of this fruit family seem to be more readily suscep- 

 tible than many of the wild species. Certain species, such as the 

 Haw (CrataBgus spp.) and Shadbush (Amelanchier Canadensis), are 

 subject to the disease when artificially inoculated with the germ. 



The researches of Savastano 1 on the tubercle of the olive tree in 

 Italy also aptly illustrate the relation of immunity and resistance. 



1 Savastano : Tuberculosi, iperplasie, e tumori dell' olivo : Ann. R. Scuola Sup. 

 d'Agric., Vol. V, 1887. ^T\ 



ur 



