DAILY RHYTHMS IN CERTAIN ROOTS 
across the section back from the growing point a distance equal to twice 
the diameter of the root). This reciprocal relation between elongation and 
cell division in the root as a whole might be explained on the same basis as 
that in the individual cell, provided there is a coordination within the 
root tip sufficient so that when a large number of cells are undergoing mitosis 
the total energy available within the tip is directed more to mitosis than 
toward growth and elongation, and hence the one process will be near its 
maximum when the other is near its minimum. Whether it be a matter of 
available energy or not, the fact remains that the two processes, elongation 
and cell division, do alternate with each other, both in the individual cell 
and in the root as a whole. Since neither process can go on for any con- 
siderable length of time to the exclusion of the other, the curve representing 
the extent of either will show waves such as those found in the present work. 
Thus, activity once initiated by the beginning of germination of the seed or 
bulb, these two processes, of necessity having a definite relation to each 
other, bring about the rhythms here found. 
The fact that these rhythms have a definite interval in the various 
series of the same variety of seedlings, and that corresponding waves in the 
different series bear the same relation to each other as the time interval 
betw^een the times of initiation of metabolic activity, i.e., that the maxima 
and minima in the different curves depend for the time of their appearance 
upon the time when germination was begun, indicates that the ultimate 
cause of this alternation between mitosis and elongagion is entirely an 
internal cause and not related to external conditions and is in perfect accord 
with the above suggested energy hypothesis. This harmony in the various 
series of plants of the same variety shows, further, that the rhythms here 
found are not mere chance variations in activity which, when plotted, show 
such curves, but rather that the two processes, elongation and cell division, 
follow each other in a regular manner, the root tip being occupied with one 
and then with the other, and hence showing a regular and definite oscillation 
from the one to the other. 
Whether or not this reciprocal relation existing between elongation and 
cell division is sufficient entirely to account for these rhythms, and whether 
there might not also be other rhythms independent of, and more or less 
confused with, these first rhythms, is a question not satisfactorily answered 
by the data at hand. The fact that the times of maxima of elongation in a 
few cases did not coincide with the times of the minima of cell division might 
seem to indicate that there were other factors influencing the course of these 
activities in the plant besides the alternation of elongation and cell division. 
It is conceivable that a relation might exist between growth activity (in- 
cluding mitosis) and available food supply, whereby these metabolic pro- 
cesses might, once initiated, gradually increase and finally outweigh the 
capacity of the enzymes to render stored food available. Then, with a 
lessening proportion of available food, a slowing down of these processes 
