ee fe ob ~ ws - - 34 ~— — 
KeELLicorr: PERIODICITY IN ROOT OF ALLIUM 531 
2. The primary maximum occurs shortly before midnight 
(11 p.m.) and the primary minimum about 7 a.m. The second- 
ary maximum occurs about 1 p. m. and the secondary minimum 
about 3 p. m. 
3- There is no correspondence between the rate of cell-divi- 
sion and slight variations in temperature. 
4. In the root of Podophyllum, maximal and minimal points 
occur at almost the same hours as in A//ium. 
5. Tap-water alone or with various substances in solution, 
seriously affects the course of cell-division. In some cases there 
may be recovery and partial return to the normal condition. 
6. Under normal conditions of growth, the rate of elongation 
of the root of AM/ium exhibits a daily rhythm showing two maxima 
and two minima during twenty-four hours. 
7. Elongation is most rapid (primary maximum) about 4 or 5 
P.m., the secondary maximum occurring about 7 a. m. The 
primary minimum is about 11 p. m. and the secondary minimum 
about noon, 
8. Periods of rapid cell-division coincide with low rate of 
clongation, and during rapid elongation the rate of cell-division is 
lowest. 
3- Methods 
(@) CELL-DIVISION 
Sound average-sized bulbs of A//imm were selected and allowed 
to germinate at ordinary room-temperature in moist sand or pine 
Sawdust until the roots were from 50 to 100 mm. in length: this 
was usually after from four to six days. Then at definite inter- 
Vals, usually of about two hours, throughout 24-hour periods, 
two root-tips from different parts of the bulb were taken for exami- 
Nation. The tips were fixed 20 minutes in acetic-alcohol (glacial 
acetic I part, 70 per cent. alcohol 2 parts), sectioned longitudinally 
10 microns thick, and stained in Delafield’s haematoxylin. 
It is believed that the method used in determining the relative 
Numbers of dividing cells in the different tips entirely obviated 
error due to differences in the size of the tips. From each, the 
three sections passing nearest the axis of the root were selected 
and the area to be examined determined in the following way. At 
