Enportuia CANKER OF CHESTNUT 593 
summed up: ‘‘ From these records it will be noted that the minimum 
temperature for all was 9° C. and that all failed to grow at 7" ©. The 
maximum temperature for Endothia parasitica . . . was35°C. 
The optimum appears to be near ordinary room temperature, that is, 
about 22° to 24° C.” 
Tannic acid 
Since the chestnut tree has a relatively high tannic-acid content, the 
question naturally arises as to the relation of tannic acid to the growth 
of the fungus. Clinton (1913:407) grew the fungus on cultures contain- 
ing various amounts of tannin, and summarizes his results thus: ‘‘ (1) Both 
fungi [referring to E. parasitica and E. gyrosa] 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 FE. gyrosa. (3) Long- 
continued cultivation of the parasitic variety in artificial cultures without 
tannic acid probably 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.” Clinton suggests that the tolerance of a higher percentage of 
tannin probably bears some relation to the parasitism of EF. parasitica. 
ECOLOGIC RELATIONS 
Murrill (1906 a:153) gives his opinion (1) that winter injury possibly 
accounted for the epiphytotic, (2) that there was a decline in constitutional 
vigor, because of coppicing, which predisposed the tree to attack, and 
(3) that cultural conditions could determine relative resistance to attack. 
The effect of these ecologic conditions, as well as of drought, in increasing 
the susceptibility of the tree is upheld by Clinton (1909:887-889; 1911: 
717: 1913:389-407). In the last publication Clinton (1913:390-391) 
writes: 
“ Now, if the condition of the host bears no relation to the rise and spread 
of the disease, the writer knows of no satisfactory explanation for its sudden 
and destructive appearance in this country except its importation from 
some foreign country. The evidence to date, however, is very strongly 
against the idea that it is an imported pest, as we shall show later. Among 
the farmers in Connecticut who have been able to watch this disease 
rather closely there are many who believe that the weakened vitality 
