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the more alamdaiU sijriiig wood but always within the canker excrescence 

 prosenchyma wood in contrast to parenchyma wood. The illustration 

 shows the last formed, dark rings in the health}- part divided radialh' 

 toward the diseased part, n indicates a diagonall\ cut, dead branch. 



This lu.xuriance of growth, 

 which manifests itself by the 

 formation of the radiating canker 

 excrescence, ma}' not, howe\er, 

 lead universally to the conclusion 

 that the growth of the tree as a 

 whole is always luxuriant. On 

 the contrary, a regular occur- 

 rence of canker knots is found in 

 weak, slender trees in certain 

 localities. 



Cankered and abo blighted 

 trees usuall}- show a \er} luxuri- 

 ant lichen growth. At the central 

 place of attachment of such 

 lichen cushions it ma}- often be 

 proved that the cork layers of the 

 branch have been separated and 

 the thailus cords shoxed in be- 

 tween them. In fact I could 

 obserxe cases in which the lichen 

 thailus penetrated the whole pro- 

 tect i\e cork laver f)f the branch 

 and reached the collench\-matous 

 l)ark cells, some of which still 

 contained chlorophyll. The lichen 

 growth may, therefore, not be as 

 injurious as the yellow and green 

 forms are generally declared to 

 be. How much, however, the 

 spread of the lichen depends upon 

 some indi\ idual peculiarity of the 

 tree is still unknown to us (prob- 

 abl}- a greater tenderness, poros- 

 it}- and torn condition of the 

 bark ), as is explained by an obser- 

 vation on grafted older trunks of hVaxinus. The stock, possibly one to one 

 and a half meters tall, appeared only scantily covered with lichens while 

 the grafted scion, which at times bore a 1.2 to 15 year old crown, was closely 

 covered by lichen growth. As a rule, cankered places on old ash trees, 

 standing on wet ground, are coxered with lichen. 



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