CYTOLOGy 



6-18 



(1940) suggested that the ribose nucleoproteins originated from the 

 heterochromatic regions of the chromosomes. 



MITOSIS 



Pretreatment of cells by fluoride followed by treatment with di- 

 ute toluidine blue has revealed structures in the vacuole which I iden- 

 tified as chromosomes. Fig. 6-12 shows 5 or 6 pairs of rihromo- 

 Somes in the vacuole. Fig. 6-13 shows two foci of a cell in which 

 six pairs of chromosomes were counted. Fig. 6-15 shows six hap- 

 loid chromosomes in the nuclear vacuole of a spore. Fig. 6-16 

 shows the fusion of nuclear vacuoles in copulation. Fig. 6-17 shows 

 paired chromosomes in the nuclear vacuole of newly formed zygotes. 

 Fig. 6-18 is a Feulgen stained preparation (by Rafalko) showing that 

 the vacuole contains Feulgen positive chromosomes. Fig. 6-19 shows 

 a series of photographs of yeast cells stained with toluidine blue. 

 On the basis of these and similar observations I have proposed that 

 yeast mitosis occurs according to the steps shown in fig. 6-20. 



Fig. 6-12 Paired Chromosomes Stained with Toluidine Blue, 



Observations of living cells have shown that the chromosomes 

 in the non-dividing cell are each attached by one end to the inner 

 wall of the vacuole and wave around in the nuclear sap. They seem 

 to be relatively rigid and are apparently rather evenly spaced about 



