KELLICOTT: PERIODICITY IN ROOT OF ALLIUM 537 
tends to recur when the disturbing factor is removed or overcome. 
The fact that the specific cause of the disturbance is unknown in 
this instance does not lessen materially the value of the evidence. 
(c) Comparison of observations on Podophyllum.—\We may 
now review briefly the results obtained from a similar examination 
of the rhythm of cell-division in the root of Podophyllum. This 
form was selected to be compared with Ad/ium because it too had 
very large cells, rapidly and easily grown roots, and because it 
was a representative of a totally different subclass. The method 
used was the same as with A//ium, except that the plants were 
Benes 
ECCCUREREE 
NOAA AL. 
W \/ ie a \ 
OLE OO ee ae eg aie a 
p. mM. a. mM. 
FicurE 3. Cell-division in root of Podophyllum. t, temperature. 
germinated in moist sphagnum, thoroughly rotted and washed. 
The results obtained from two series of root-tips cut every two 
hours, are shown in FIGURE 3, together with the record of the 
temperature of the surrounding air. These curves show more 
extensive minor variations than did those of A//iwm, but it is re- 
markable how closely similar are the curves obtained from the 
two plants. Even the minor variations of the main curve are 
always of the same nature, differing only in extent, with the single 
€xception of the period from 4 to 6 p. m. when one curve began 
to ascend shortly before the other. 
Underlying these minor fluctuations there are the general 
Waves of cell-division, most clearly marked in curve I. These 
show primary maximum and minimum at midnight and 6 p. m. 
