ATYPICAL MITOSIS AND OTHER NUCLEAR PHENOMENA 185 



undergo mitosis side by side, the two spindles often uniting to form only 

 two daughter nuclei. Examination of the chromosomes in such pairs of 

 mitotic figures shows that each nuclear portion after amitosis has only a 

 portion of the full complement, and that certain chromosomes have been 

 fragmented in the amitotic division. The two portions together con- 

 stitute a complete complement. Since some fragments may pass to the 

 poles along with the unbroken chromosomes, the union of the mitotic figures 

 brings about a partial restoration of the original nuclear organization. 



These phenomena suggest that the common failure of amitotic nuclear 

 fragments to undergo mitosis is due not so much to the effects of amitosis 

 itself as to a persistence of the abnormal conditions which originally 

 induced amitotic division. Were such nuclei to continue dividing in a 

 growing and differentiating tissue, derangements in their nuclear organi- 

 zation might well be reflected in abnormalities in the results of differen- 

 tiation; and were descendants of such nuclei to be transmitted through 

 gametes to the next generation, abnormalities in development would be 

 expected there also. The basis for such an expectation is seen in the 

 known results of chromosome fragmentation and translocation to be 

 described in Chapter XVIII. At present it has not been shown in any 

 case that the descendants of true amitotic nuclei ever become the nuclei 

 of functional gametes. 



Induced Aberrations of Mitosis. — Aberrations of mitosis like those 

 so often mistaken for amitosis may be induced by a considerable variety 

 of means. For example, when root tips and other plant tissues are 

 subjected to the action of chloral hydrate and other anesthetizing agents,* 

 the normal course of mitosis is disturbed in various degrees, depending 

 on the strength of the dose. As a rule the achromatic figure develops 

 poorly or not at all, and the chromosomes become irregularly scattered 

 in the cell (Fig. 108). They may form one or more groups and reorganize 

 nuclei which often remain connected by bridges or undergo fusion. 

 Hence it is not uncommon to find in such tissues all gradations between 

 normal mitosis and what looks like amitosis. The latter condition is 

 known as " pseudoamitosis" (Haecker). Nemec and Sakamura attribute 

 such scattering of chromosomes to protoplasmic streaming induced by 

 the experimental agency; this is in harmony with G. Ritter's (1911) 

 observation that the nucleus may sometimes be displaced by streaming 

 induced by the wounding of near-by cells. The experiments of Van 

 Regemorter indicate that the failure of the spindle substance to develop 

 a regular figure in chloralized tissue is due to a destruction or impairment 

 of the cell's polarity, the recovery from the effect of the reagent involving 

 a return to the properly polarized condition. 



* Pfeffer (1899), Nathansohn (1900a), NSmec (1904, 1910a, 1929c), Kemp (1910), 

 Sakamura (1920), Van Regemorter (1926). The effects of many other agents are 

 described by Yamaha (1927o6). 



