CYTOLOGy 6-2 



homologous to the smaller standard centrioles found in inverte- 

 brate eggs. The present analysis of the yeast nucleus suggests that 

 the similar structure in the yeast cell carries the heterochromatin 

 in addition to the centriole and we have called the entire complex 

 the "heterochromatinic centrosome." This may also be the case 

 in Neurospora, although no Feulgen stains of the Neurospora nucle- 

 us have been reported. The extensive genetical study of this or- 

 ganism in recent years has not been accompanied by equally inten- 

 sive study of the nuclear apparatus; the recent work of McClintock 

 has been concerned with the enumeration and description of the 

 chromosomes rather than with the other problems of nuclear struc- 

 ture. 



Wager and Peniston's description of the yeast nucleus corres- 

 pond in many respects to Harper's description of the nucleus of 

 Phyllactinia. They called the deeply staining eccentric structure 

 attached to the nuclear vacuole the "nucleolus"; we have identified 

 this structure as the "heterochromatinic centrosome." They showed, 

 and we have confirmed this finding, that the chromosomes are often 

 polarized to it in the manner characteristic of most fungal nuclei. 



Our observations agree rather well with those of Wager and 

 Peniston (1910). Fig. 6-1 which summarizes their findings, is re- 

 produced herewith. 



Table 6-1 lists the designations which they gave the different 

 organelles along with the name applied to the same structures by. 

 Guilliermond, Janssens and Leblanc, and Lindegren. Wager and 

 Peniston' s interpretation was limited by contemporary concepts of 

 cell structure, but their drawings reveal an organization easily im- 

 derstandable in terms of modern concepts of the nucleus. 



Janssens, who discovered chiasmata, and Beijerinck agreed 

 with Wager and Peniston in characterizing the large vacuole in the 

 yeast cell as the nucleus. However, Guilliermond, in a polemic 

 with Wager and Peniston ridiculed the significance of their analy- 

 sis and insisted that only the deeply staining eccentric structure 

 attached to the vacuole was the nucleus. There was a general ac- 

 ceptance of Guilliermond' s interpretation because this eccentric 

 structure (which we call the "heterochromatinic centrosome") is 

 easy to demonstrate by the crudest cytological methods and because 

 it has been fovind to be Feulgen -positive by a number of workers 

 including Margolena, Badian, and more recently Delameter. The 

 chromosomes themselves, however, are extraordinarily delicate 

 and difficult to make visible with most ordinary techniques, and 

 when the cell is killed with Carnoy or other substances contain- 

 ing large amounts of acetic acid, the nuclear vacuole usually dis- 

 integrates and only the densely staining centrosome is foimd in the 

 cell. In fact, cjrtologists like Kater and Henneberg, who also 

 demonstrated the same chromatinic threads in the vacuole as those 



