1922.] Immunity Trials of Potatoes, 1921. 



1147 



fully planted with Victorias, of which the majority are worked in 

 the usual way on the Myrobalan stock ; these are considerably 

 infected. The remaining trees have been worked on another 

 stock (probably the common plum), in such a way that most 

 of the trunk of the tree belongs to the stock. The habit of 

 growth of these trees appears to have changed very consider- 

 ably, and apparently they are highly resistant. Further inocu- 

 lation experiments made by Mr. Brooks have shown, that while 

 the Pershore variety can be readily infected with the disease, 

 there is a high percentage of natural recovery. The results 

 of these experiments are very encouraging. 



Mr. Brooks sounds a note of warning with regard to the 

 propagation of plum trees. He has noticed cases in which 

 silvered suckers have been used for propagation, and as he 

 rightly points out, trees raised from diseased suckers are doomed 

 from the commencement. 



As regards methods of control, Mr. Brooks is convinced that 

 the adoption of a proper system of plant sanitation, the import- 

 ance of which cannot be over-estimated, is undoubtedly effective. 

 Infected wood and all dead wood must be cut out and 'burned 

 without delay, and the wounds thereby made must be protected 

 immediately by a covering of grafting wax, tar, or similar 

 material. Apart from the removal of diseased and dead wood, 

 the less plum trees are cut about the better. It does not suffice, 

 however, merely to burn the infected material cut from the fruit 

 trees. Careful attention must also be devoted to those non-fruit- 

 ing trees in the vicinity of plum plantations on which the fructifi- 

 cations of the fungus are commonly found. It should be remem- 

 bered that Poplar trees, which are often planted as a wind 

 screen, are susceptible to Silver Leaf disease when cut back, 

 and that their dead stumps often constitute centres of infection. 



All growers of fruit trees are strongly recommended to take 

 action on the lines indicated above. 



The Potato Immunity Trials were continued in 1921 at the 

 Potato Testing Station of the National Institute of Agricultural 

 Immunitv Botany at Ormskirk, Lancashire. The tests 

 Trials werS carried out by Mr. H. Bryan, B.Sc, 



Q j Superintendent of the Station, on lines laid 



Potatoes, 1921. do ™ b >" the Mb***- 



The season generally was peculiar 



because of the continued drought and the excessive heat, and 



