(Vor. 11 
88 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
they do indicate the zones in the major portions of which the 
fungi show good growth. Тһе optimum range as indicated 
in any 1 solution does not always foretell the range which will 
be obtained in any other solution, for if the one solution is more 
favorable for growth than the other, the range will tend to be 
widened, producing a curve with a slightly fluctuating optimum 
zone covering several Pg units. 
Furthermore, the optimum range varies slightly with the 
temperature. А temperature too high or too low for maximum 
growth tends to affect the physiological balance of the fungus, 
resulting, no doubt, in а narrower optimum range or a range 
shifted a little toward either neutrality or greater acidity. Such 
a case is well illustrated by Polyporus adustus (fig. 8), Polystictus 
versicolor (fig. 14), and Daedalea confragosa (fig. 4). It is impos- 
sible to foretell just how a certain species will react toward а 
given set of conditions; therefore it is not practicable or even 
possible to point out any marked optimum Ру or even a narrow 
range of Ри in which the optimum will invariably fall. 
The directions of the changes in the initial acidity due to 
growth vary with the solution and with the temperature. In 
general, growth in the Richards’ solution tends to increase the 
acidity. However, Polyporus adustus decreases the acidity of 
this medium in the more acid range, while minor variations from 
this general increase are to be noted for Pholiota adiposa at 
15° C. and 25? C. and for Pleurotus ostreatus at 15° C. In no 
case, however, are these exceptions pronounced. 
This tendency toward increased acidity is not characteristic 
of the fungi in the peptone solution. Lenzites sepiaria is the 
only species to increase the acidity throughout the entire Ри 
range and at all temperatures. Polystictus versicolor in gen 
also causes an increase in the acidity of this solution. On the 
other hand, in marked contrast to its action in the Richards’ 
solution, Pleurotus ostreatus decreases the hydrogen-ion concen- 
tration in every case. For the other 5 species the results are 
not uniform, but on the whole the active acidity is decreased 
within the initial range Py 2.5-5.5 and increased within the 
initial range, 6.5-8.0. P, 6.0 in the majority of cases remains 
close to the initial, varying little in one direction or the other 
with the different fungi. : 
