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 their 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 Penicillium glaucum on grape sugar is 31° C; 

 on salts of formic acid, 35° C; and on glycerin, 36° C. 



Hoffmann (13) states that in the case of Merulius lachrymans 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 tune, 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, 



