CHESTNUT BARK DISEASE. 433 
4 per cent. tannic acid, the growth of the fungi tends to form 
a more or less firm coating over the surface, after the manner 
of growth on the solid medium. Above 4 per cent. the growth 
becomes gradually less evident, generally showing in floating 
patches, embedded masses, or lateral growths around the side 
of the glass. Finally, at the highest percentages, 10 to 14, growth 
entirely ceases, only one having been successful at the latter 
strength in any of the tubes. 
(5) In the higher percentages of tannic acid E. gyrosa shows 
an enfeebled growth sooner than does var. parasitica, since at 
6 to 8 per cent. it makes comparatively little growth, correspond- 
ing to that made by the variety at about 10 per cent. It gen- 
erally fails entirely to make any growth at above 10 per cent., 
or only a poor growth above 8 per cent. in most of the tubes; 
.while the variety in only one case made any growth above 12 per 
cent. and rarely any but a poor growth above Io per cent. 
(6) At the higher percentages the difference in the appear- 
ance of the two fungi is less marked than at the lower, so that 
from 4 per cent. up, where spore production of the variety is 
largely cut out, they are scarcely to be distinguished. 
(7) There was some variation in development with the dif- 
ferent cultures of the same fungus in the higher percentages of 
the tannic acid, as shown by one of the cultures of var. par- 
asitica from Connecticut which had been in artificial culture for 
over three years failing to grow quite as-well as the more recent 
cultures. These variations are perhaps not constant. 
(8) All the preceding notes relate to cultures that were inoc- 
ulated from plain potato-juice agar directly onto those contain- 
ing various percentages of tannic acid. Another set of cultures 
was made in which each was brought up gradually through all 
the lower percentages of tannic acid. In these it was found that 
this gradual acclimatization to the tannic acid gave a somewhat 
more luxuriant growth of both fungi at the higher percentages 
than when transferred directly from the potato-juice agar to 
these. 
Later experiments based on the preceding results were made 
with all our cultures of E. gyrosa (26 in number) and those of 
var. parasitica (22 in number), using two cultures of each and 
the following percentages of tannic acid: 4.0, 6.0, 8.0, 10.0. 
These cultures showed, as in the previous tests, that the variety 
