Fig. 5-2. Yeast Cells Stained with Lugol's Solution Showing 

 the Centrosome Attached to the Vacuole. The vacuole is lobed but 

 the centrosome maintains an attachment with all lobes. 



Fig. 5-1 Two Different Optical Sections through a Cluster of 

 Yeast Cells Which Have Just Begun to Bud. These cells were photo- 

 graphed with the Spencer phase-difference microscope. In the rest- 

 ing cells in the center of the cluster, the mitochondria are very 

 clear, with sharply delimited borders. Fewer and smaller mito- 

 chondria appear in the budding cells at the edges of the cluster, 

 showing that the granules become dispersed in the cytoplasm of an 

 activated cell. 



With the Spencer phase-difference lens the mitochondria are 

 visible either stained or unstained and it has been possible to 

 corroborate the findings of Caspersson and Brandt regarding their 

 appearance in resting cells and their disappearance in active cells 

 This lens has given us a marked advantage over other workers, such 

 as Wager and Peniston, and Gui 1 liermond , who used ordinary light 

 microscopes, and whose work was done before Caspersson and Brandt 

 had worked out the cyclical appearance and disappearance of the 

 mitochondria. Since many stains dissolve or obscure the mitochon- 

 dria, differences of opinion concerning their position or presence 

 are understandable. They might easily be confused with volutin if 

 large numbers are present, because the volutin stain, as devised 

 by Meyer, requires destaining and this is always erratic through 

 the yeast cell wall. 



5-4 



