238 SCIENCE AND FRUIT GROWING 



only a slight difference between the various sets, and that was 

 against the dressing 



of 



lib ....... 65 



Jib ....... 70 



Nil ...... 72 



Similar results were also obtained in the case of trees which 

 were not inoculated till after they had been planted 



ilb ...... 39 



Nil. . . 34 



Subsequent experiments in which a daily dressing of J oz. of 

 sulphate per tree, together with liquid manure, was given, 

 failed to bring about the recovery of any of the silvered trees 

 on which it was tried. 



In combating any disease, the method in which it spreads 

 is the most important point to be determined. All these inocula- 

 tion experiments with stereum prove conclusively that this 

 disease is a wound disease, the fungus spores entering through 

 some opening in the bark ; but whether it could spread in any other 

 way, had to be determined. To see if it could be carried from one 

 tree to another in the absence of active fungus spores, and in the 

 ordinary operations of pruning, two row r s of plum trees were 

 planted, with only two feet between the rows; one row was 

 inoculated, the other was not. In pruning these, cuts were 

 made alternately on the silver-leafed trees and on the sound 

 ones, but in no single case did the latter become affected by the 

 disease. Further evidence that the disease cannot be communi- 

 cated in this way is afforded by the various plum hedges at 

 Wo burn, for, here and there in these, isolated cases of stereum have 

 occurred ; but the disease has not spread from the tree affected to 

 the neighbouring ones, in spite of the hedges having been pruned 

 from one end to the other, regardless of the presence of the 

 diseased trees. Evidence accumulated from many growers was 

 also emphatic in showing that the various diseased trees in a 

 plantation, though often not far from each other, were generally 

 not contiguous. Of course, if in pruning trees, the pruning in- 

 strument happens to collect actual fungus spores from any active 

 stereum, inoculation of the next tree on which it is used would 

 probably follow ; and hence in pruning a plantation where 

 stereum exists, it is well to sterilise the pruning tool by 



