6 BULLETIN 227 , U. S. DEPARTMENT OF AGRICULTURE. 
substances must be added if further growth is desired, and the addi- 
tion of each nutrient substance introduces a new factor of error. 
Unlike bacteria, which can be grown well in synthetic liquid media 
of known composition, wood-destroying fungi prefer a more complex 
and solid medium for then satisfactory development. This latter, 
as a rule, consists of a mixture of meat broth and sugars solidified 
by agar-agar or gelatin. 
Various investigators have used different types of media and dif- 
ferent methods, and this accounts in large part for the variability in 
results. Some, as Clark (3), have used simple plant decoctions, 
others bouillon, and still others a nutrient agar or gelatin modified in 
various ways as to available carbon and nitrogen. 
Le Renard (16), in his work on Penicillium crustaceum, shows that 
toxicity is closely associated with the composition of the medium 
and in the same medium varies somewhat with its concentration. 
Likewise the presence or absence of certain constituents may 
determine the temperature which an organism will endure on dif- 
ferent media, for Thiele (27) has shown that the maximum tempera- 
ture for the growth of PenidUium gJaucum on grape sugar is 31° C; 
on salts of formic acid, 35° C; and on glycerin, 36° €. 
Hoffmann (13) states that in the case of Merulius laeJirymans a slight 
growth takes place even at 30° C. on certain liquid media, while on 
solid media (5 per cent agar-agar) the fungus was killed at that tem- 
perature. He likewise thinks that as a fungus becomes accustomed 
to a certain culture medium in its development it gradually over- 
comes certain unfavorable conditions. 
So far as the writers are aware at the present time, the media most 
satisfactory for the growth of wood-destroying fungi are not free 
from the objection of being complex, variable, and more or less 
unknown in their chemical composition; however, certain synthetic 
media are being developed in the course of the work which show 
promise of being satisfactory. In an effort, however, to secure results 
comparable as far as possible with those of certain European investi- 
gators, such as Malenkovic and various workers at Munich, and also 
Rumbold in this country, the malt-extract agar medium used by 
these workers has been adopted. This medium will be described later. 
EFFECT OF ADSORPTION ON TOXICITY. 
The apparent diluting effect which inert, practically insoluble 
matter exerts on toxic substances has been often observed. For 
instance, the injurious effect of poisons is not so noticeable when 
seedling roots are placed in sand and watered with toxic solutions 
of definite concentration as when grown directly in such solutions. 
This phenomenon of the removal from solution of a part of the toxic 
substance by nearly insoluble material, such as glass, quartz, pottery. 
