264 CARL C. LINDEGREN 



extended to enclose the bud at all times. The vacuolar process follows the 

 external surface of the centrosome into the bud, lying between the cell wall 

 and the centrosome. 



Figure 16.3-5 shows a cell in which the bud vacuole has received its two- 

 stranded chromosome complex. This is an exception to the rule that the 

 chromosomes usually are completely destained in the differentiation by 

 iron alum. 



In Figure 16.3-6 the bud vacuole is lobed. This is a rather common phe- 

 nomenon. The cytoplasm has passed into the bud and completely surrounds 

 the centrosome and the bud vacuole. The extension of the centrochromatin 

 along the surface of the acidophilic centrosome has begun. 



Figures 16.3-7, 16.3-8, and 16.3-9 show cells in which the separation of 

 the centrochromatin has been completed with mother and bud held to- 

 gether by the centrosome. 



In Figure 16.3-10 the division of the centrosome is complete, but both 

 centrosomes are near the point of budding. In Figure 16.3-11 the bud cen- 

 trosome has reached the distal end of the bud while the mother cell centro- 

 some still lies in the neighborhood of the point of budding. In Figure 16.3-12 

 both centrosomes have reached the distal ends of the cells and are prepared 

 for the formation of the next bud. 



CONCLUSIONS CONCERNING EXTRACHROMOSOAAAL INHERITANCE 



Cytological examination of the yeast cell shows that many of its organelles 

 may have the same integrity and continuity in time that characterize the 

 chromosomes — they cannot arise de novo. In the yeast cell there are seven 

 or eight such "continuous" organelles. The cell membrane, the nuclear 

 membrane, the centrosome, the centrochromatin, the cytoplasm, the mito- 

 chondria, and the chromosomes are permanent cell structures. Because they 

 apparently divide in a manner which does not provide for precise trans- 

 mission of specific portions to each daughter cell, it appears that the other 

 components differ from the chromosomes in a significant manner — they are 

 probably homogeneous, or their heterogeneity is simple, possibly a few 

 different types of dipolar molecules held together in a specific manner. 



There is no reason to assume that any one of these components is of more 

 importance, or directs the "activities" of any one of the other components. 

 The cell can function only if all its component parts are present in proper 

 structural correlation and in adequate amounts. There is no reason to as- 

 sume that any one of these components is unique in the manner in which it 

 reproduces itself. The present hypothesis proposes that they all reproduce 

 by the simple accretion of molecules like those which they contain, and it is 

 their association with each other in an adequate milieu which provides the 

 molecules necessary for their increase in size. Each of the different organelles 

 is rate limiting in growth. When any one is present in less than the minimal 



