212 



INTRODUCTION TO CYTOLOGY 



As a result of his recent researches on chloralized cells (Fig. 76) 

 Sakamura (1920) interprets all such unusual types of nuclear division as 

 those described by Hertwig and Wasielewski as the effect of disturbed 

 mitotic division, but denies the claim of those authors that such types 

 of division represent actual transition stages between amitosis and 

 mitosis. True amitosis he regards as a fundamentally different process, 

 and as essentially a degeneration phenomenon. 



D 



F 



Fig. 76. — Abnormal mitosis in chloralized root cells of Vicia. 



A, chromosomes distributed irregularly in cell. B, scattered chromosomes beginning to 

 assume nuclear form. C, nucleus reconstructed by scattered chromosomes. D, scattered 

 chromosomes reconstructing 3 separate nuclei. E, chromosomes reconstructing 2 nuclei 

 connected by bridge. F, amitosis-like appearance resulting from condition shown in E. 

 {After Sakamura, 1920.) 



On the contrary, Des Cilleuls (1914) reports that in the rabbit 

 periods of amitosis and mitosis succeed each other regularly in the same 

 cell lineage without affecting the vitality of the cells. In his opinion, 

 therefore, amitosis does not necessarily place the stigma of senescence 

 upon the cell. A similar conclusion is reached by Arber (1914), who finds 

 amitosis supplementing mitosis in the early growth stages of the leaves 

 and adventitious roots of Stratiotes aloides; and by McLean (1914)-, who 

 asserts that it is the sole method of nuclear division in the cortical 

 parenchyma of several aquatic angiosperms. Saguchi (1917) likewise 

 states that the nuclei in the ciliated cells of vertebrates divide by amitosis 



only. 



Amitosis and Heredity. — One of the most important theoretical ques- 

 tions raised by the phenomenon of amitosis is that of the effect which 

 the process may have upon the hereditary mechanism of the cell. Ac- 

 cording to the chromosome theory of heredity and development in its 

 usual form it has been thought that, although amitosis may occur in 

 connection with an altered metabolism in cells not to undergo further 

 differentiation, mitosis must occur exclusively in the germ cell lineage, 

 in order that the chromosomes and the hereditary elements they con- 



