530 Ketticotr: PERIODICITY IN ROOT OF ALLIUM 
of slowest growth . . . were the approximate moments of inser- 
tion of the septa, and consequently, moments when elongation 
would be going on with the least rapidity... .” Concerning 
the correlation of these processes in higher forms nothing at all is 
known. 
Not only has there been no real attempt to correlate the 
processes of elongation and cell-division in a given organ, but 
there is a complete lack of knowledge concerning the course of 
cell-division alone in a growing part. And while much is known 
with regard to the daily rhythm of elongation or growth of organs, 
in nearly every instance the organ observed has been aérial and 
therefore subject to very profound and rapid environmental dis- 
turbances accompanying the alternating conditions of day and 
night. As far as can be discovered the only observations on the 
daily periodicity of growth of subterranean parts are those of Strehl* 
on the roots of Lupinus, and MacMillan + on the potato-tuber. 
It seems, therefore, that here is an opportunity for profitable 
investigation : to determine whether there is a rhythmic daily 
variation in the rate of cell-division of a growing organ ; to deter- 
mine whether there is a definite daily rhythm in the growth or 
elongation of a subterranean part which is growing under much 
more uniform conditions than the aérial parts ; and finally, if such 
rhythms are found to exist, to determine whether there is any 
correlation between the processes of cell-division and elongation. 
The observations described in this paper were designed to attack 
these questions, and it is believed that the results have been defi- 
nite enough at least to warrant further serious investigation. 
I wish to take this opportunity to express my very consider- 
able indebtedness to Dr. C. C. Curtis, Columbia University, under 
whose direction these observations were carried out, for his ever 
ready aid and valuable counsel. 
2. Summary 
The principal facts brought out in this paper are the following * 
. Inthe root of A//iwm there are two maxima and two minima 
in the rate of cell-division during twenty-four hours. 
: 2) an 
Strehl, R. eoeoees iiber das Lingenwachsthum der Jer Wurzel und des 
hypokotylen Gliedes. Leipzig 
t MacMillan, C. On the sean: periodicity of the potato-tuber. Am. Nat. 25° 
462-469. 1891. 
