1902.] 



NATURAL SCIENCES OF PHILADELPHIA. 



477 



and iu its immediate neighborhood (fig. 18). The patliological 

 conditions set up by these hyplite have been described, but ini^addi- 

 tion to the increase of the bast and tlie wood, we have an increase 

 in the number of cells in the cortex and the bark. The course of 

 the liyplise and their distribution throughout the swellings will be 

 described more in detail. A brief mention at this point suffices to 

 draw attention to them. 



The Plugged Tracheids. 



The wood of the abnormal regions of the stem shows in addition 

 to the hyphffi brown -colored spots which are absent iu stems of 

 normal proportions. Without discussing at this juncture the nature 

 and significance of these brown spots, which are due to the plug- 

 ging of the tracheids, it is appropriate to discuss the distribution of 

 the spots throughout the diseased regions of the stems. Plugged 

 tracheids are found in the swellings with sixteen rings of growth, 

 beginning with the fourth annual ring of wood. Here they are 

 seen in the spring wood. Counting the number of such plugged 

 tracheids in a half-circle of the fourth annual ring of wood and in 

 the rings of successive years of the same stem, we obtain the follow- 

 ing numerical statement : 



Table IV. 



An inspection of the table shows that in small swellings the 



