114 Brown.—Experiments on the Grozvth of 
The amount of staling shown by a particular organism varies from one 
medium to another and is dependent upon the amount of the particular 
medium present. Figs. 4 and 5 illustrate this point. 
Fig. 4 gives the daily growth-rates of Sphacropsis on apple extract 
agar (A.A.), and potato extract agar (P.A.). In each case the medium is 
presented in large or small quantity by varying the depth of pouring. In 
one set the plates are deep (about 1 cm.) and in the other shallow (about 
2 mm.). The ordinate corresponding to each plotted point represents the 
average daily growth since the preceding reading. The points brought out 
by this graph are : (1) that there is distinct staling on potato agar, but none 
on apple agar; (2) that the rate of spread of the cultures on shallow potato 
agar is much less than on the deep medium, whereas both shallow and deep 
platings grow at approximately the same rate on apple agar. 
A large number of experiments have been performed on the same lines 
Fig. 4. Sphaeropsis malorum on apple agar (deep Fig. 5. Fusarium sp. on apple agar 
and shallow) and potato agar (deep and shallow). (deep and shallow). 
as those illustrated in Fig. 4, and it is possible to generalize. When the 
depth of medium is varied, it is found that the rate of growth on the deep 
and shallow plates is at first identical. If the fungus does not stale on that 
particular medium, the rates of growth on the deep and shallow plates 
continue the same. If the fungus stales, then the rate of growth on the 
shallow plates after some time is different from that on the deep plates. In 
the present case the growth on the shallow plates lags behind the deep ones, 
and this is the rule on most ordinary media. But there are interesting ex¬ 
ceptions to this rule which will be described in a subsequent paper. 
This method of comparing the growth on deep medium with that on 
shallow has proved to be of great value, as one can obtain a good idea from 
inspection of the two sets of cultures as to how far staling is taking place. 
Fig. 5 gives the growth of Fusarium on apple agar. In this case there 
is obvious staling on the shallow plates, though it had not appeared in 
a pronounced form in the deep plates. This experiment illustrates the 
