The daily periodicity of cell-division and of elongation in the root of 
Allium 
WitLiaAmM E. KELiicotr 
CONTENTS 
PAGE 
I. Introduction . ... west 52 
2. Summary......... 530 
3. Methods ,. 531 
4. Daily periodicity of cell-division 533 
A. Under normal conditions 533 
(a) Description of typical observation 533 
(4) Comparison of other observations 535 
(¢) Comparison of observations on Podophyllum...... Levaxtees 537 
B. Effects of sotationie 250 ko ee ee 538 
5. Daily periodicity of elongation 543 
(a) Description of typical observation 544 
(4) Comparison of other observations,............+.csseereeneeeees 545 
6. Relation between cell-division and elongation 549 
1. Introduction 
It is a well-known fact that rhythmic variation in the rate of 
growth is widespread, perhaps universal. It is similarly known 
that the nature of the rhythm varies considerably in different 
plants, so that there is no uniform hour at which the rate of growth 
is highest or lowest: each form seems to have its own peculiar 
rhythm. Perhaps this is one reason why there is at present so 
little uniformity of opinion among those who have studied the 
phenomena of growth in various plants, as to the factors in- 
volved in the production and maintenance of this rhythm. One 
Possible factor has been overlooked almost entirely, namely, that 
of cell-division. As a matter of fact very little is known concern- 
ing the actual relations between cell-division and growth. Prac- 
tically the only record of any observed correlation between cell- 
division and elongation is that of Ward,* who observed that, in 
Bacillus ramosus, ‘the period of cell-division entails more or less 
cessation of growth ”’ (page 294), and that (pages 301-2) ‘periods 
--*Ward, H. M. On the biology of Baci/lus ramosus (Fraenkel), a schizomycete 
of the river Thames, Proc. Roy. Soc. 58: 265-468. 1895. 
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