PLANTS IN THEIR RELATION TO DISEASE. G7 



in diameter. Those will spread. I have seen them spread 

 in one season so that they covered the entire trunk, and 

 girdled it. Then we have the ordinary effects of girdling ; 

 the tree will die. That is, if the diseased part penetrates 

 into the living part. I have also seen cases where the tree 

 was so vigorous that a new growth of bark was formed ; 

 the strength of the tree was suQicicnt to throw off that dead 

 portion. Then we have what appears to be new bark formed 

 under the dead bark, and so we may have these conditions 

 repeated continually. It is evidence of that character that 

 leads me to believe that the disease is constitutional and ex- 

 ists in the sap long before its appearance in the blighted limb. 



QuESTiox. Do you consider that there is any better rem- 

 edy than to, remove the tree and replace it with a new one ? 



Prof. Peniiallow. Before I decided upon that, I should 

 want to make a strong effort to cure the tree. 



Question. What would be your remedy ? 



Prof. Pexhallow. I should apply sulphate of potash as 

 a special fertilizer around the roots, in connection with sol- 

 uble phosphates. 



Question. AVhat would be your advice as to the quan- 

 tity to be applied to a tree five or six years old ? 



Prof. Peniiallow. From 100 to 150 pounds to the acre ; 

 say three or four pounds to a tree, if the tree is not very 

 badly diseased. If badly diseased, I would apply more. 



Question. Don't you suppose there is more than one 

 cause of blight in pear trees ? 



Prof. Penhallow. I dare say ; and very probably it is 

 developed by a multiplicity of causes. When we come to 

 lack of nutrition as one of the- primary causes, of course 

 we have got to take other things into consideration. 



Question. Would not frozen sap have a tendency to 

 produce it? 



Prof. Penhallow. That might tend to its development. 



^Ir. — . I noticed, several years ago, when I had some 



small branches that were affected by this borer, by cutting 

 them off I escaped any further trouble. 



Prof. Penhallow. The action of the borer would be 

 more sure of introducing the disease after the decay of the 

 sun'ounding tissues. 



