CHESTNUT BARK DISEASE. 407 



year to year according to external conditions more or less 

 favorable for its production. 



In our tannic acid culture work with the true chestnut blight 

 and its close ally, Endothia gyrosa, reported in detail later on, 

 we found: (i) Both fungi can use tannic acid, at least in 

 small amounts, as food, shown by the blackening of media 

 through oxidation, loss of acidity, more luxuriant growth, with 

 a low per cent, of the acid added, than without it, and a slight 

 growth on agar-agar with tannic acid as the available source 

 of food. (2) Higher percentages of tannic acid (four per 

 cent, and above) are detrimental to a vigorous growth of 

 either of these fungi, and finally (10 to 14 per cent.) entirely 

 inhibit their growth. But with the true blight the tolerance 

 is apparently greater by 2 to 4 per cent, than that of the 

 saprophytic E. gyrosa. (3) Long-continued cultivation of the 

 parasitic variety in artificial cultures without tannic acid prob- 

 ably lowers its tolerance to the higher percentages of tannic 

 acid. (4) Gradually passing these fungi in cultures from the 

 lower to the higher percentages of tannic acid apparently 

 raises their tolerance to it. 



From the results of these cultural experiments and what we 

 have been able to learn about tannic acid in the chestnut, we 

 reason that the true chestnut blight is better able to become an 

 active parasite on chestnut trees than the Endothia gyrosa. Any 

 cause that would lower the tannic acid, etc., content of the 

 trees would allow it to develop into a more vigorous para- 

 site, and its gradual tolerance to this higher percentage of 

 tannic acid would give it an added virulence up to a certain 

 extent. With the return of the tannic acid, etc., content of 

 the tree above this limit of tolerance, the fungus would gradu- 

 ally revert to a less virulent and finally to even an inconspicuous 

 parasite. 



PREVIOUS CHESTNUT TROUBLES. 



Nature of the Troubles. It is well known that in times past 

 the chestnut trees in this country have suffered severely in cer- 

 tain districts, particularly in the South, in some cases being 

 practically exterminated, so that their range is now consider- 

 ably lessened from what it was originally. Strangely enough, 

 no one has surely accounted for any of these devastations. 



