DAILY RHYTHMS IN CERTAIN ROOTS 
401 
is a very close reciprocal relation existing between elongation and cell 
division. A single large divergence occurs in the case of the 7 P.M. mini- 
mum of cell division in curve 13. 
Allium Cepa. In table 12 the maxima and minima of elongation and 
cell division in Allium Cepa are compared. In the case of roots from bulbs 
we find, again, very nearly a reciprocal relation between rapidity of elonga- 
tion and number of cells undergoing division. Another divergence is seen 
in the case of the 3 P.M. minimum of cell division in both curves 10 and 24 
(or 7-9 P.M. maximum of elongation). 
Table 12. Comparison of Maxima and Minima of Elongation and Cell-Division in Allium 
Cepa 
Roots from Bulbs 
Elongation Maxima 
(see table 4) 
Cell Division Minima 
Curve 10 
Curve 24 
Elongation Minima 
Cell Division Maxima 
Curve 10 
Curve 24 
7-1 1 A.M. 
7 A.M. 
7 A.M. 
1-5 P.M. 
I P.M. 
II A.M.-5 P.M. 
7-9 P.M. 
3 P.M. 
3 P.M.-7 P.M. 
9-1 1 P.M. 
9 P.M. 
II P.M. 
1-3 (5) A.M. 
I A.M. 
I A.M. 
3-7 A.M. 
5 A.M. 
5 A.M. 
Roots from Seeds 
Elongation Maxima 
(see table 5) 
Cell Division Minima 
Curve 12 
Elongation Minima 
Cell Division Maxima 
5-9 A.M.-(ii A.M.) 
7 A.M. 
11 A.M. 
I P.M. 
1-3 P.M. 
5 P.M. 
3-5 P.M. 
7 P.M. 1-5 A.M. 
3 A.M. 
9 P.M. 3-7 A.M. 
9 P.M. 5 A.M. 
In the case of roots from seeds all of the maxima and minima of cell 
division find corresponding minima and maxima respectively in elongation 
so that the reciprocal relation here is quite evident except for the extra 
fourth wave in elongation. 
In general we may say that the times of maxima of elongation are near 
the times of minima of cell division and vice versa in all plants studied. This 
reciprocal relation is not so clearly expressed as in the case where both pro- 
cesses may be observed at the same time and in the same individual cell as 
Ward (38) found in Bacillus ramosus Fraenkel and de Wildeman (39) found 
in Spirogyra; but is probably as near as might be expected from the fact 
that the two processes must be observed, not only in different cells, but also 
in different individual roots. 
Discussion 
The question naturally arises : What are the causes of the rhythm found 
both in the elongation and the cell division of the plants studied? That it 
may be due to external influences of changes in illumination and temperature 
