i 26 Brown.—Experiments on the Growth of 
container) in order to see in the former all the distinct morphological 
features associated with staling, while the latter shows none of them. 
The question of the intermingling or non-intermingling of two fungal 
colonies (of the same or of different species) is intimately connected with 
the question of staling. The only physiological interpretation of the non¬ 
intermingling of two colonies is that by the combined action of the two 
colonies the zone of medium immediately between them becomes so stale 
to both fungi that neither of them can cross it. The phenomenon is not 
one of absolute incompatibility, and investigation would probably show 
that any fungus could be made to intermingle with any other under appro¬ 
priate conditions. In the case of species which have an intense staling 
action, it would, of course, be much more difficult to find such conditions 
than with species which have only a feeble staling activity. The question is 
obviously one of the chemical nature of the various staling products and of 
the manner in which they may be rendered ineffective. 
That intermingling or the converse is a relative matter can be easily 
demonstrated. If two colonies fail to intermingle under a given set 
of circumstances, any alteration of the latter which tends to reduce staling 
will tend to produce intermingling. Thus, if two colonies planted at 
a certain distance apart fail to meet, they can be made to intermingle by 
reducing sufficiently the distance between the two inocula. Also, while two 
colonies may meet when sown at a certain distance apart on a deep medium, 
they may fail to do so when grown under like conditions on a shallow layer 
of the same medium. Again, intermingling or non-intermingling can be 
determined by simply manipulating some of the staling factors, e. g. the 
gaseous factors discussed in the present paper. Table XI illustrates an 
experiment with Sphaeropsis along these lines. The top row of figures in 
the table represents the number of days from the start of the experiment; 
the figures below represent the shortest distance from the margin of one 
colony to that of the other ; the medium was potato agar in Petri dishes. 
Table XI. 
Closed dishes in air : 0. 
5 . 
/• 
8. 
9 - 
12. 
i 5 - 
I 7 * 
Deep medium 7.0 
i -7 
met 
— 
— 
. - 
— 
— 
Shallow medium 7-0 
2-3 
— 
o-8 
c-8 
0.8 
o -75 
Open dishes in container in air: 
Deep medium 7-0 
1.25 
met 
— 
— 
— 
— 
_ 
Shallow medium 7-0 
1.85 
0.25 
met 
— 
— 
— 
— 
Open dishes in container in 7- 
5 %C 0 2 : 
Deep medium 7.0 
1.1 
met 
— 
_ 
— 
— 
_ 
Shallow medium 7-0 
1.4 
met 
— 
— 
— 
— 
— 
