THE MITOTIC CYCLE 



authors to which reference has just been made are at an early stage, it 

 is clear that they are likely to yield new information of the interrelation- 

 ships of the nucleus and cytoplasm during mitosis. The importance of 

 this topic needs no emphasis. 



Inhibition of cytokinesis 



In plants, this stage in the mitotic cycle is highly susceptible to arrest. 

 The phragmoplast, by means of which the new cell wall is formed is an 

 orientated body (p 146) and it is interesting to see that this, like the 

 spindle which precedes it, is sensitive to colchicine; Wada^^^ has 

 observed the dissolution of the phragmoplast in the living staminal 

 hair-cell of Tradescantia in the presence of this alkaloid. Simonet and 

 GuiNOCHET^^^ found that halogenated derivatives of benzene and 

 toluene suppressed cytokinesis in seedlings of Linum while nuclear 

 division continued, multinucleate cells were thus formed. These 

 authors refer to this effect as the 'paradichlorobenzene type of response' 

 from the name of the compound which was first found to provoke it, 

 though other workers (Gavaudan et alii'^^^) have found that in the 

 roots of Triticum the action of these substances is not entirely restricted 

 to this phase of cell division. Kihlman^^^ ha^ shown that cytokinesis 

 is suppressed in the meristems of Allium roots by treatment with adenine, 

 or with methylated purines. Adenine has a similar effect on chick 

 ceils in culture (Hughes) (Plate XV (2b) ). Chalkley^^' finds that a 

 variety of agents which interfere with locomotor activity in Amoeba 

 prevent the fission of individuals in mitosis, while nuclear division 

 proceeds unhindered. The suppression of cleavage by chemical treat- 

 ment and the formation of a di-diploid nucleus was first demonstrated 

 by WiLSON^^^ in 1902, who treated sea-urchin eggs with ether. 



However, it has been shown by Shigenaga^^^ that the formation of 

 the cell plate in Tradescantia petal cells is readily disturbed by treatment 

 first with a narcotic and then subsequently with hypotonic sucrose or 

 water. Shigenaga's work is a beautiful illustration of the Japanese 

 cytological tradition of work with living material, and the photographs 

 which accompany his paper show very clearly how these treatments 

 can result in several grades of effect. Either a single di-diploid nucleus, 

 or two diploid nuclei may be found within an undivided cell, or an in- 

 complete septum may form between the two daughter nuclei. Since 

 changes in hydration probably occur in both nucleus and cytoplasm 

 during telophase, it may be that the miscellaneous chemical agents 

 which affect this stage of cell division act by interfering with the normal 

 movements of water at this time. 



A number of substituted hydroxybenzene derivatives have been 

 shown both to inhibit cell division in marine eggs, mainly of Arbacia 

 and also at the same time to stimulate respiration (Figure 69). (The 



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