1202 RESISTANT PLANTS 



are clearly distinguished from the others by their high degree of resistance 

 to the attacks of Thielavia basicola. These plants were covered with hoods 

 to ensure self-pollenation ; they were numbered and noted, and the seeds 

 of each of them were sown separately on special ])lots. 



Type " White Burley ". — The experiments relating to this were under- 

 taken at Ontario. On the plantations of '' White Burley, " " mongrels " 

 or " Green Burley " specimens are sometimes met with, which are distin- 

 guished by the decided green colour of their leaf-stalks and ribs, which, on 

 the other hand, are whitish in colour in normal plants. The green plants 

 resist the disease better than the others. Some of them being isolat- 

 ed and reproduced in pure lines, were found to be resistant and true to 

 type, while others split up into green and white. It was possible to isolate 

 from the latter, resistant types such as " B 1193 ", the resi.stance of which 

 in infected soil may exceed one hundred times that of the common " Bur- 

 ey " (relative resistance 42.6 and 0.5 respectively) and " P 701 B " which 

 is not yet fixed, but already promises well. 



" Cigar Binder Leaf " Type. — The experiments in relation to this were 

 conducted at Madison. The best types " Comstock Spanish " and " Con- 

 necticut Havana " are going more and more out of favour with planters 

 and are replaced bA^ types resistant to Thielavia, such as Seedleaf ", " Big 

 Seed ", "H3'brid " (as representatives of these latter types see table ; 

 "Page's Comstock", "Pease Seed " and " Northern Hybrid " which neve- 

 rtheless give a product somewhat inferior in quality). 



In the plantations of Wisconsin, as already stated, 45 specimens were 

 isolated, the progeny of which were studied and tested during the period 

 1913-1915. The data collected cannot be used for instituting compari-sons, 

 because the infected soil was so fertile that it yielded a crop in excess of 

 that of the sterilised soil. They at any rate show the possibility of obtaining 

 b}^ individual selection, superior types having at the same time a high de- 

 gree of resistance. 



935 - Resistance of Pyrus calleryana to Necrosis of the Bark and Branches (Ba- 

 cillus a mylovorus). — See No. 870 in this Bulletin. 



936 - Studies on the Resistance of Prunus spp. to Bacterium tumefaciens. — 



Smith (1. Clayton., in Phytopathnlos,y, Vol. 6, No. 2, pp. i86-i')4, PI. VI. Baltimore, 

 Md.,ii»i(). 



Experiments were undertaken with a view to .studying the degree of 

 resistance to Bactemnn tumefaciens in the different species and varieties 

 of fruit trees of the genus Primus. This bacterium is, as was proved by the 

 researches of Erwin F. Smith, the primary cause of the hypertrophied forma- 

 tions on the branches and twigs, which are known under the name of " crown 

 gall" (I). . " 



All the .species of Priiiins are not equally liable to contract this di-sease, 

 and it must not be considered impossible to find and fix practically immune 

 types which might serve as a basis for a progressive renewal of the orchard, 



(i) See B. Feb. 191.5. No. I^5. (Ed.). . 



