THE MITOTIC CYCLE 



It is difficult to see more in the last sentence than a declaration of 

 faith in the sense in which St. Paul defines the word (Hebrews xi. i). 



When two authors generalize in this way from two different points 

 in the same field, a controversy may develop, in which each may well be 

 right as far as his own observations are concerned. Whits'^ puts the 

 point very well in a comment on a debate concerning the state of the 

 chromosomes in telophase: 'The protagonists on both sides of this 

 polemic seem to have tacitly assumed that whichever opinion was true 

 must also be true in all types of cells.' 



Those who do this run the risk of neglecting the counsel which in the 

 sister field of genetics was given by Bateson,^ and which surely is 

 just as relevent to cell biology: 'Treasure your exceptions! . . . Keep 

 them always uncovered and in sight. Exceptions are like the rough 

 brickwork of a growing building which tells that there is more to come 

 and shews where the next construction is to be.' 



Mitosis seems to me to be a supreme example in science of diversity 

 within a unity. It can hardly be doubted that the cycle of the formation 

 and dissolution both of the chromosomes and of the spindle are basically 

 similar throughout all the varying divergencies of detail which accom- 

 pany these events in diflferent organisms. Probably insufficient notice 

 has been taken of these differences, though studies such as those of the 

 ScHRADERs' havc shown how revealing these aberrant features can be. 

 It would be desirable to extend such investigations from the purely 

 descriptive level and to combine the second and third of the above 

 categories, and thus to begin the comparative physiology of cell division. 

 Here lies a potential approach of great power to the analysis of mitosis, 

 which could be pursued consciously if we attempted to define what 

 basic factors in addition to the visible events in nucleus and cytoplasm 

 are common to mitosis, wherever the process is found. 



In recent years much has been learnt froni the detailed study of 

 individuaUtypes of cells with various techniques, but it has yet to be 

 shown how far these findings may be applied elsewhere. Above all, we 

 need to know more about the physiology of mitosis in the plant cell; 

 it would be particularly desirable to study topics such as the proteins 

 of the chromosomes, the growth of the orientation of the spindle, and the 

 cytoplasmic events during cytokinesis such as the changes in permea- 

 bility of the cell membrane. Experience in other aspects of cell 

 physiology has already shown the need for the student to surmount the 

 conventional academic divisions of biology, which in this field have 

 unquestionably impeded its progress. 



REFERENCES 



1 Baker, J. R., J. Qiiekett., micr. Club., Ser 4, i (1943), 256 



2 Hughes, A. F., International Revue of Cell Biology (in the press) 



210 



