6-7 THE YEAST CELL 



Badian's failure to locate the vacuole makes it difficult to interpret 

 his work, although it seems probable that he is describing the het- 

 erochromatin rather than the chromosomes. 



Levan (1946) has recently shown that the structure of the centro- 

 some is more complex than was originally proposed by Badian. 

 However, he agrees with Badian (and disagrees with me) in calling 

 it the "nucleus." Badian's drawings of the centrosome reveal it as 

 a bipartite body; Levan found it contained a maximum of ten bodies 

 which he called "chromosomes." Renaud (fig. 6-3) also discover- 

 ed the centriole in the centrosome, which I have not yet seen 

 by my techniques, Levan used the Feulgen technique, while Renaud's 

 preparations were made with iron hemotoxylin, I have been able to 

 confirm Renaud's concept of the linear arrangement of the particles 

 of chromatin in the centrosome by alkali -toluidine blue stain. The 

 findings on the division of the centrosome are very similar to those 

 of Renaud. Renaud has shown two clearly visible small centrioles 

 which precede the chromatin in the division of the structure which I 

 have called the centrosome. 



THE HETEROCHROMATIN 



The structure of the centrosome is clearly shown by the alka- 

 li-toluidine blue stain (fig. 6-4). This stain reveals the structure 

 \^^ich Levan, Badian, and Renaud described as chromosomes. It 

 usually stains structures in the centrosome only. As many as 20 or 

 more small particles can be seen in each centrosome and careful 

 focusing shows that they are connected by threads. In some cells 

 only 2 dense rods are found suggesting that long threads have coiled 

 down to form the rods. A bridge connects two cells in division 

 showing that this is the same material as that shown to divide by 

 transverse fission in the cells stained with aceto-orcein (fig. 5-3). 



I have identified this densely staining, Feulgen positive material 

 as heterochromatin since it divides by transverse division and there- 

 fore could not compose the chromosomes. Furthermore, Rafalko 

 has succeeded in staining the chromosomes within the nuclear vacu- 

 ole with the Feulgen stain and I have described their mitosis so it 

 If no longer necessary to insist that this Feulgen positive material 

 is chromosomal in character. 



MECHANISM OF BUDDING 



Budding is a unique method of cell division; I have shown (1945, 

 fig. 6-5) that it is the direct result of the extension of a tube from 

 the vacuole to a point on the cell wall where a very tiny protuber- 

 ance is formed on the outer surface of the cell into which the vacu- 

 ole-tube passes and in which it enlarges to form the bud-vacuole. 



