444 J- MCA. KATER. 



the cytologist and the geneticist. It seems remarkable that the 

 investigation of nuclear division in yeast has not previously 

 attracted the attention of cytologists, as well as mycologists. 



In the earlier work on Phaseolus it was found that the linin 

 strands radiating from the nucleolus are actually the linin 

 sheaths of chromosomes which persist through the resting 

 condition and give the chromosomal vesicles morphological 

 individuality during interkinesis. It seems probable that the 

 linin strands of Saccharomyces are of the same nature. The 

 collection of chromatin along them in the early prophase (Fig* 

 16) and the bulge between them in the telophase (Fig. 25) 

 would indicate this. However, since the actual transformation 

 of the prophase nucleus into chromosomes and the alveolization 

 of early telophase chromosomes could not be followed with any 

 degree of certainty a definite statement of chromosomal con- 

 tinuity in yeast cannot be made on a morphological basis as in 

 Phaseolus, but the probable homology is certainly worthy of 

 mention. 



The existence of radiating linin strands alone would not 

 justify this interpretation, since they are present in many 

 protozoan nuclei where the nuclear membrane remains intact 

 throughout mitosis. In such organisms the membrane is not a 

 product of the linin sheaths of chromosomes, as in higher animals 

 and plants, and the linin strands could not easily be interpreted 

 in the same manner. Such a nucleus is found in Polytomella 

 citri (Kater, 1925). In Saccharomyces the nuclear membrane 

 disappears and consequently it is quite possible that the linin 

 strands are homologous with those of Phaseolus. 



SUMMARY. 



The nucleus of Saccharomyces cervicix divides by mitosis in the 

 process of budding. 



The chromosomes apparently form, divide, separate, and give 

 rise to daughter nuclei in much the same way as in Phaseolus. 

 The linin strands connecting the nucleolus and nuclear membrane 

 probably represent sheaths of chromosomal vesicles. 



