The Division of Saccharomyces cerevisiae Using Carbon Replicas 



269 



Fig. 3. Two cells broken apart before ready to divide. Shad- 

 owed carbon replica. (By courtesy of tiie /. Roy. Microscop. 

 Soc.) Magnification 14,000. 



before division. Two lines can be seen crossing the 

 "neck" indicating that a rim has formed within the 

 cell wall. In figure 3, a cell has been mechanically 

 broken away from its parent before it was ready to 

 divide, and an internal rim can be clearly seen, 

 together with the broken cytoplasmic connection. It 

 is thus possible to say that in the division process, 

 two internal rims form in the neck connecting the 

 two cells before the formation of transverse mem- 

 branes which must be present when the cells are 

 ready to divide. Now if a hypothetical longitudinal 

 section is drawn of a birth scar and a bud scar and 

 these are inverted over each other, it will be found 

 that they key together. Thus it is possible to propose 

 the sequence of events shown in figure 4. (a) shows 



Oouqhher 



Daughher 



Porenh 



Fig. 4. Diagrams of hypothetical longitudinal sections 

 through the "neck" joining two cells illustrating structural 

 changes during the division process. (By courtesy of the 

 J. Roy. Microscop. Soc.) 



Fig. 5. Electron micrograph of ihin section through the 

 "neck" illustrating the key mechanism. (After Agar and 

 DoLiglas, by courtesy of the J. Bacleriol.) Magnification 

 X 21,000. 



the first stage in the formation of the internal rim 

 and in ih) the rims are nearly completely formed be- 

 fore the transverse membranes, in (c) the interlocking 

 scars are shown in section. These sections arc easily 

 deduced by studying the electron micrograph in 

 figure 1. id) shows the last stage in the process as 

 proposed by Barton (2) in which the birth scar on 

 the daughter cell grows outwards, thus releasing the 

 key mechanism. 



An independant investigation by Agar and Doug- 

 las (I), who examined sections of yeast concurrently 

 with the present work, showed that the above con- 

 clusions are in agreement with information provided 

 by sections. The key mechanism is well illustrated 

 in the micrograph of the section shown in figure 5. 

 This work is more fully described elsewhere by 

 Bradley (4). 



in addition to the study of yeast cells, the carbon 

 replica has been applied to the study of the surface 

 structure of some bacillus spores. These are e\en 



Fig. 6. Carbon replica of spores of B. brevis. Magnification 

 X 25,000. 



