90 Colchicine 



side are arrested. Under these conditions further development is 

 arrested, and chromosomal bridges extend between the cells.^^ 



Direct destructive action upon cell plates was recorded also in 

 wheat root tip cells. Generally, the absence of spindle determines 

 the formation of a restitution nucleus precluding any form of c)to- 

 kinesis as well as daughter nuclei/^=^- ^^- ^^' ^^^ ^" The interrelation 

 between cytokinesis and mitosis is shown by the effects of colchicine. 



By centrifuging root tips treated with colchicine, a much greater 

 displacement of chromosomes against the centrifugal wall was found 

 among treated cells than among the controls. The action of the drug 

 was interpreted as an effective lowering of c)toplasmic \iscosity. 



Allium root tips treated with colchicine at varying exposures were 

 centrifuged to determine changes in structural viscosity of the achro- 

 matic figure. The decrease in \iscosity was indicated. Moreover, 

 there was a low viscosity at eight hours, when c-mitosis was at a peak. 

 After return to normal bipolar mitosis the viscosity showed increases 

 paralleling these recovery processes. 



Another view somewhat opposed to that expressed above has been 

 presented. Since the spindle fibers are inhibited and no achromatic 

 figure is present to hold the chromosomes in position, greater dis- 

 placement may take place regardless of \iscosity change. The centri- 

 fuge tests merely show that the spindle fibers are lacking. Supportmg 

 this \iew are the obser\ations on cyclosis in Elodea, which does not 

 seem to be changed by colchicine. 



Additional tests showing changes in viscosity among plant cells 

 are reviewed in Chapter 4. 



:}.'j—^: Cytoplasmic (O)istitueuts and cell organUes. The centro- 

 some, a self-perjietuating Ijody outside the nucleus, becomes involved 

 with spindle destruction. Its activities are depressed along with 

 those of the si)indle mechanism. Several centrosomes may accumulate 

 within a cell treated with colchicine, hence the formation of multiple 

 stars. Each star probably represents a centrosomic body. These were 

 carefully demonstrated in Triturus xnndescens. 



A confusion arises from the mitochondrial picture and colchicine. 

 Some say these bodies are affected b\ the drug;i'^^' others report no 

 change.-^ The concentrations as well as materials vary widely, but it 

 would seem that some consistent reaction might be obtained. Ho\\- 

 ever, until now we can only re\ ie^v the j)ro and con. Modifications 

 involving fragmentation, dispersion, reduction, as well as minor 

 morphological changes have been seen after colchicine treatments 

 directed to: (1) Flexner-Jobling carcinoma of rat, (2) liver cells 

 of rat,^i-^- (3) cells of certain orthoptera, GyrUiis assimilis and 

 Mflanoplus diffeyentialis.-''' No mitochondrial modifications are re- 

 ported for neuroblasts in Chortojjiiaga vindijasiata;'^ an observa- 



