38 



[Vol. 6 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



Twenty-five-cc. portions of the filtered and unfiltered medium 



were then placed in 1000-cc. 



a 



Nonsol 



>» 



Erlenmeyer flasks 



containing a pinch of CaC0 3 , plugged, capped with beakers, 

 and autoclaved. The flasks were inoculated according to 

 method B described previously (p. 27), the suspension be- 

 ing prepared from a 6-day-old slant of the Fi 8 culture. 

 The cultures were incubated for 10 days at 28-30° C. Part 

 of the flasks were placed on the mechanical shaker and part 

 were kept on the shelf near by. The plan and results of the 

 experiment are shown in table xm. 



TABLE XIII 



MODIFIED ASHBY'S MEDIUM WITH .15 PER CENT AGAR AS PROTECTIVE COLLOID 





No. 



Treatment 



Nitrogen 



(mgs.) 



Unfiltered 



Shelf 



103* 

 104* 



105 

 106 



Check 

 Check 



Inoc. 

 Inoc. 



0.17 

 0.13 

 1.57 

 1.70 



Shaker 



107 

 108 



Inoc, 

 Inoc. 



1.16 

 1.39 



Filtered 



Shelf 



79 

 80 

 81 

 82 



Check 

 Check 

 Inoc. 

 Inoc. 



0.16 

 0.12 

 2.45 

 2.39 



Shaker 



83 

 84 



Inoc. 

 Inoc. 



1.94 

 2.30 



* 300-cc. 



A dupli 



flasks used. 



cate experim< 



ent was carried o 



ut simultaneously, 



with all conditions the same except that no agar was used in 

 the nutrient medium. The results appear in table xiv. 



The results show that when a small amount of agar is added 

 to a medium in such a way that it may act as a protective col- 

 loid, this medium then is not affected injuriously by filtering. 

 On the other hand, if the agar be omitted, the filtered medium 

 is distinctly inferior to the unfiltered. Moreover, in the pres- 

 ence of the agar the shaker is apparently of no benefit to the 

 growth of the microorganisms. 



