1902.] 



NATURAL SCIENCES OF PHILADELPHIA. 



473 



the cells of the inedullarv rays, are usually of a greater diameter 

 thau the normal, which also accounts for the greater width of the 

 rings formed at the canker. These observations agree with those of 

 Anderson" upon the canker growth produced by Dasyscypha resin- 

 aria. The medullary rays of the swollen areas of the stem seem 

 to increase somewhat in diameter. This increase of diameter is not 

 due to the increase in the number of parallel rows of cells, but is 

 due to the increase in diameter of the single row of parenchyma 

 cells which is met with in the normal cross -section. These cells 

 stain more deeply than the normal cells because of the granular 

 contents. Further reference to this change of content in the 

 medullary ray cells of diseased sections of the stem will be made 

 with a description of the longitudinal section of the diseased 

 regions. 



If a number of tracheids in the annual rings of the swollen area 

 of the sixteen years of growth be compared with the table display- 

 ing the number of tracheids in the annual rings of twenty-one 

 years' growth, a wide difference is at once observable. TJie num- 

 ber of tracheids in the abnormal growth is clearly greater thau in 

 the normal one. 



Table III. 



' " Anderson, Alexander P., Dasyscypha reslnaria causing canker 

 growth on Abies balsamea in Minnesota, Bulletin of the Torrey 

 Botanical Club, XXIX, pp. 23-34. 



