66 MORPHOLOGIC VARIATION 



curred shortly after this increase in length, and in repeated cell divi- 

 sions it is observed that the cells become progressively longer before 

 each division. The new cells formed are free of granules, but the 

 granules present in the original tip cell remain, and can be seen 

 throughout the subsequent periods of observation. After some five 

 hours growth, the number of cells began to increase greatly so that 

 it was difficult to follow individual cells, but the original tip cell was 

 still easily distinguished, and repeated divisions of this portion of the 

 colony were followed for several hours longer. 



In studying these developing micro-colonies, two rather interesting 

 features are observed, other than the changes in size and form of 

 the cells. One particularly evident in the second micro-colony, is 

 the apparent tendency for growth to be restricted to the end of a 

 chain of cells as long as the cells remain in a chain. This is reminis- 

 cent of the terminal growth of the filaments of mycelium in molds. 

 It is not clearly distinguished in micro-colonies or in cultures from 

 solid media, where the chains, durmg the period of active growth 

 at least, quickly break up; but in preparations from broth cultures 

 this is very frequently clearly evident; long chains of cells are formed 

 in which the two terminal cells are found to be much longer than 

 other cells in the chain. The second feature is the mechanism by 

 which the chain is broken and the cells are separated. This is par- 

 ticularly evident in the first two micro-colonies. It is seen that 

 after a cross wall has formed, the two cells bend at right angles, 

 so that the cells are finally torn apart by the leverage of their pres- 

 sure against each other. This mechanism has been previously des- 

 cribed in spore forming bacteria. It is also noteworthy that the ac- 

 tively growing cells are free of granules, though those granules which 

 were present in the original cell at the beginning of growth may be 

 retained at the tip, which serves to identify it through the subse- 

 quent periods of observation. 



The third micro-colony developed from five cells. It will be ob- 

 served that for a period of three hours there was practically no evi- 

 dence of growth. One of the cells developed a cross wall, and one 

 of the daughter cells so formed proceeded to disintegrate. Another 

 became deformed, developing a constriction at one end, with an ac- 

 cumulation of granular material in the constricted portion. At the 



