^13 



constitution of their walls, transverse in curves (np) the hypertrophied tis- 

 sue, v^hich, at the beginning, contains starch. 



This formal and functional organization of the bark parenchyma which 

 determines the formation of the bark may be found also in other tree barks, 

 but first occurs, so far as I have observed, in the older axes in which the 

 bark parenchyma has been influenced by the pressure of the bark scales 

 lying above it. On this account I have called these bands of tangential cells 



S 



Fig. 26. Spot on the trunk of an apple tree with the tan disease. Explanation of 

 the letters in the text. (Orig.) 



(np) "Pressure bands," which later suberize, often also developing plate 

 cork cells and cutting off the bark scales. 



I have had opportunity to study the tan disease in young cherry branches 

 in a wet summer on very vigorous young trees in a nursery. Figure 2y 

 shows that on these cherry branches the outer bark had split or been torn 

 open in broad, irregular stripes (e). An intense yellow ochre colored mass 

 (/) could be recognized at the ruptured spot, which, when tapped vigorously, 

 gave off a powdery dust. The whole impression given by these branches 

 was as if they had been very thickly covered with rust fungus. 



