AMERICAN CHESTNUT BLIGHT 697 



Briefly stated the hope for the future of chestnut as a forest propo- 

 sition lies, the writer believes, in the possibility that the species is now 

 actually developing immunity in its struggle with the parasite. The 

 young sprouts are the battle ground, and the older infected areas are 

 one vast natural laboratory in which is being worked out, before our 

 eyes, the problem of the survival of chestnut. What facts and indica- 

 tions support such a hypothesis ? 



The Significance of Hypertrophy 



In looking over the diseased trees on the ground and in studying the 

 charts in publications there appear definitely two distinct types of 

 canker. One is shrunken in appearance and shows a very marked 

 depressed surface on the bark (atrophy), the other is characterized by 

 a swollen distorted appearance (hypertrophy). What does this mean? 

 Can one not read from these two distinct indications a decisive dif- 

 ference in the reaction of the respective hosts to the parasite? In 

 the first it would seem no resistance is met, while in the second a 

 struggle is going on — a decided resistance to the invader is made. 

 (For an illustration of these two types of canker see Plate 37 of 

 Bulletin 347,* Cornell Agricultural Experiment Station, and Plate 1, 

 Bulletin 380, U. S. Department of Agriculture. The latter is interest- 

 ing as the figure showing the sunken canker indicates developing 

 resistance as the disease progresses — note the hypertrophy at the 

 edges). 



The hypertrophied cankers are not an infrequent occurrence. A 

 number of observers have noted them. Graves,' as already stated, 

 gives them as evidence of resistance. Collins" has reported this form 

 also, and the writer (1920) noted a number of hypertrophy cankers 

 in eastern Pennsylvania and northern New Jersey. 



Another point is, that these cankers (the hypertrophy type) are 

 invariably found on young, vigorous or rapidly growing sprouts or 

 branches — just the place where one would expect a struggle to occur. 

 Rankin" states : "On young rapidly growing coppice, however, swollen 

 areas (hypertrophy cankers) with the bark split open lengthwise are 

 commonly found." Anderson and Rankin* (at page 549) say: 

 "Cankers on rapidly growing limbs are usually outlined by a distinct 

 ridge of slighty hypertrophied tissue." In the Pennsylvania chestnut 

 tree blight commission's report for 1912 are shown two figures of 



"Manual of Tree Diseases, VV. H. Rankin, at page in, lois. 



