H. G. Thornton 



263 



The effect of reducing the asparagine content below 0-05 per cent, is 

 shown in Fig. 10, where the increases in area of surface growths of B. 

 dendroides on media containing 0-05 per cent., 0-005 per cent, asparagine 

 and no asparagine, are plotted. It will be seen that while the growth is 

 reduced in the total absence of organic nitrogen, the reduction of aspara- 

 gine content to 0-005 per cent, was without appreciable influence on the 

 spreading. 



This reduction, however, was found to produce a significant falling 

 off in the number of colonies developing when a suspension of Rotham- 

 sted soil was plated on the two media. 



The optimum concentration of asparagine in the count medium is 

 therefore in the region of 0-05 per cent. This concentration has been 

 adopted in the medium. 



Days growth. 

 Fig. 10. -B. dendroides. Effect on asparagine content of medium on spreading. 



The additional nitrogen in the medium was supplied as KNO3 and 

 the effect of this compound on the spreading was therefore tested. The 

 medium used in this and the next experiment had the following com- 

 position, and to it KNO3 and asparagine were added in the amounts 

 indicated. 



CaClo 

 MgS04.7H20 

 NaCl ... 

 Agar . . . 



Table IV shows the areas of spreading growth of B. dendroides after 

 two and eight days incubation at 20° C. on media nitrogen supply as 

 shown. 



1-0 gm. vyctv.12 



0-2 „ FeCl3 



0-1 „ Mannitol 



15-0 „ Water 



0-1 gm. 

 0-002 „ 

 1-0 „ 

 1000 c.c. 



