548 Kewxicotr: PERIODICITY IN ROOT OF ALLIUM 
has an independent rhythm of its own in addition to a rhythm 
induced by that of the stem and other aérial parts, and offers some 
tentative explanations of both of these. The fact that here inter- 
ests us particularly is that there is frequently a double maximum 
in the rate of growth during the twenty-four hour period. Thus 
far there is agreement with the root of A/dm ; how much farther 
this agreement extends can not be stated, for MacMillan does not 
mention any hours at which these maxima occur. 
We may also compare briefly at this point, the rhythm of 
elongation of the aérial parts. Observations upon Adam have 
been made by Stebler * on the elongation of the leaf. Stebler 
found that the maximum of growth coincides with the period of 
greatest light intensity (12-4 p. m.), growth being slower during 
the night, the minimum occurring between 12 and 4a.m. His 
curves show this single wave very definitely. Many others work- 
ing on other plants have found similarly a single daily wave of 
growth, although the actual periods of maximum and minimum 
do not always correspond by any means. Thus, for example, 
Sachs} found the elongation in Dah/ia to be most rapid in the 
early morning (6-9 a. m.) and the slowest in the evening, (3-6 
p. m).; Prantl t in Cucurbita found the maximum elongation to 
occur about 3 p. m. (12-6 p. m.) and the minimum from 3 to 6 
a. m.; and, to complete the possibilities, MacDougal § found that 
in the leaf of Hyacinthus the maximum of elongation occurs 
between midnight and 4a. m. and the minimum about noon. The 
only uniformity here is the single maximum and minimum each 
day. 
Godlewski || at first observed only a single wave of elonga- 
tion in the epicotyl of Phaseolus, but later he found that there 
were definitely two maximal and two minimal periods during 
twenty-four hours. The minima occurred morning and ee 
* Stebler, F. G. Untersuchungen iiber das Blattwachsthum. Jahrb. Wiss. Bot. 
Il: 47-123. 1878. 
+ Sachs, J. Arbeiten Bot. Inst. iecdcpe ated r: 
{ Prantl, K. Arbeiten Bot. Inst. Wiirzbur 
eee D. T. Text-book of plant aa, 295. New pe 1901. 
|| Godlewski, E. Studien iiber das Wachsthum der Pflanzen. . Sree 
Akad. are Math-Naturw. Classe, 23: 1-157. (Abstract by sane "bot Central- 
, blatt, 55: 34-40. 1893. 
