CYTOLOGICAL CHANGES DURING GERMINATION 91 



Table I 



The influence of medium on the size and composition 



of the spores Bacilltis cereus varieties 



Organism Medium Av. Spore RNA-P/ DNA-P/ N/ 

 Wt. Vol. Spore Spore Spore 

 (10-i-^g.) iix^xW') (10-^«g.) (10-^«g.) (10-i«g.) 



B. cereus N.A.* 1.40 - 31.0 9.6 1500 



H&C+ 0.98 23.9# 35.6 9.8 1000 



B. cereus var. sotto [A-) N.A. 



H&C 



B. cereus var. sotto { — ) H&C 



B. cereus var. N.A. 



thuringiensis H&C 



* ^Nutrient agar (Difco). 



+ = The agar medium of Howie and Cruickshank, supplemented with 0.5% 

 casamino acids Difco. 



# = The previously published (ref. 2) value of 1.04 // for the volume of the 



spores of B. cereus is erroneously high by the factor of 5. 

 ( + ) = crystal bearing parent strain 

 (~") =: non-crystal producing mutant 

 N = Nitrogen 



27%, and var. thuringiensis 19% less RN A/spore than the same varieties 

 grown on the agar of Howie and Cruickshank. It should be mentioned here 

 that the spores grown on nutrient agar showed greater variation in size and 

 were much less stable to storage as wet suspensions than were those grown on 

 Howie and Cruickshank medium. The DNA content/spore however was not 

 influenced by the medium and seemed to be a constant for each species. Varie- 

 ty sotto ( — ) is one of several non-crystal forming variants which were se- 

 lected from platings of the crystal-bearing variety of sotto. The colony char- 

 acteristics of the sotto ( — ) were identical to those of the sotto ( + )? the only 

 distinguishing feature being the inability of the rod to produce a crystal 

 with its spore. The DNA content and volume of the spores of these two 

 sotto variants were also identical. The greater N content of the spores from 

 these cells which do not have a crystal is perhaps to be expected. 



Electron micrographs of clean spores of four of the groups gathered in 

 Table I are shown in Fig. 4, and from this type of picture reasonably ac- 

 curate calculations of spore volume could be made. 



In grouping these data on the crystal bearing strains of B. cereus we also 

 found that the largest spores were those which contained the greatest amount 

 of DNA (Table II). Thus for any given species there may be a minimum 

 space into which that cell's chromatin may be arranged. 



