A NOTE ON SPORE FORMATION 115 



cells characteristic of the resting phase of the culture, as being 

 analogous to the differentiated cells which occur in the mature plant 

 or animal. Minot states that differentiation consists essentially in 

 this, that something new appears within the cell. I submit that 

 the metachromatic granules observed in diphtheroid bacteria, the 

 unstainable granules previously described in Bacillus megatherium, 

 the spores which are found in many species of bacteria, are some- 

 thing new which appears within the protoplasm analogous to the 

 various granules, secretory or reserve material, or of unknown func- 

 tion, which serve to distinguish the differentiated cells of a multi- 

 cellular organism from their embryonic prototypes. 



It has been shown in Chapter VI that the metachromatic gran- 

 ules begin to reappear with a decrease in the growth rate, and are 

 most persistent in those cultures (heavily seeded, or dilute medium) 

 which have the lowest growth rate; which I have just shown is 

 also true of spores. Those factors then which tend to produce a 

 short growth phase of low rate tend to give a maximal development 

 of those characters which distinguish the mature or differentiated 

 cells, as conversely they tend to give a minimal development of 

 the embryonic types. 



