central position with respect to two poles and separation of the sister 

 chromatids to opposite ends of the cell. All this is somehow mediated 

 by an extrachromosomal apparatus, namely, the spindle. The questions 

 of how this mechanism evolved and of how universal it is have received 

 little attention. In the case of viruses, no such mechanism seems to exist 

 or be needed. In organisms with two or more chromosomes some method 

 of synchronization of chromatid separation would be expected, but 



'I r 



(a) (b) 



Figure 10-2. Photomicrographs Showing Mitotic-like Configurations in 

 the Mold, Blastocladiella einersonii. (a) Interphase nuclei displaying beaded 

 ring of chromatic material tightly appressed along the surface of the central 

 body or nucleolus; (b) Anaphase-like Configuration Formed by the Separa- 

 tion of Two Chromatic Masses. (From Turian, G. and Cantino, E. C, 1960. 

 "A Study of Mitosis in the Mold, Blastocladiella, with a Ribonuclease-aceto- 

 orcein Staining Technique," Cytologia, 25, Fig. 1, p. 102, and Fig. 5, p. 104. 

 Courtesy of Dr. Gilbert Turian, Institute of Botany. Geneva, Switzerland.) 



whether or not one can use mitosis as observed in the cells of something 

 like a root tip as a universal model is questionable. In the ascomycete 

 fungus, Gelasinospora, both mitotic and meiotic divisions involved in 

 formation of ascospores seem comparable in all respects with the equiv- 

 alent divisions of higher plants (Sung. Alexopoulos, and Wilson, 1954). 

 In the yeasts, which belong to the same general group, the situation is 

 more obscure. There have been continuing disputes as to the identity 

 of the various structures in the yeast cell, with the consequence that de- 

 scriptions of nuclear division offered by different workers have shown 

 marked disagreement. Subramaniam (1952) maintains that, under aer- 

 obic conditions, mitosis is essentially the same as in higher organisms 



204 / CHAPTER 10 



