KELLICOTT: PERIODICITY IN ROOT OF ALLIUM 547 
growing with less potential, such for instance as are on the descent 
from the maximum of the grand period. Ordinary stimuli would 
produce either a delayed reaction or none at all. Therefore the 
daily maximal and minimal periods are delayed and the stimuli 
usually producing the secondary waves are inoperative. 
Summarizing then in regard to elongation we may say that 
there is a daily rhythm of elongation of the root of A//ium which 
occurs in the absence of variation in illumination and independently 
of slight variations in temperature : this rhythm must be the result 
of internal factors. The daily rhythm is such that elongation is 
most rapid about 4 or 5 p.m. and slowest about 11 p.m. Be- 
sides these primary waves there are secondary points, the second- 
ary Maximum occurring about 7 a. m. and the secondary minimum 
about noon. 
It will be well to compare, at this point, these results on A//ium 
with those derived from the study of other subterranean organs. 
As mentioned in the introduction to this paper,* the only records 
are those of Strehl and MacMillan. Strehl found that there was 
a single maximal and minimal wave in the rate of elongation every 
twenty-four hours, the rate being highest about midnight and 
lowest about noon. His curves, which represent observations ex- 
tending over several days, show admirably the varying appearance 
of the daily curve depending on the phase of the grand period 
which it represents. Strehl’s observations were made upon the 
roots of Lupinus, and the conditions under which they were 
growing were far from normal ; 7, ¢., the roots were growing in 
water and were contained in glass placed only 1.5 m. from a 
West window where they would be subject to moderately strong 
illumination, 
In MacMillan’s observations upon the growth-periodicity of 
the potato-tuber, the plants were under normal conditions of 
stowth and the results are entitled to more weight. Unfortunately, 
as he himself states, his observations were of a fragmentary nature 
and were to be considered rather as a preliminary report. Mac- 
Millan concluded that the rate of increase in diameter of the 
Potato-tuber occurred rhythmically, with one, two, or perhaps 
more maxima in twenty-four hours. He believes that the tuber 
* See page 530. 
