DAILY RHYTHMS IN CERTAIN ROOTS 
size is so slight that variations in size of the part are due almost entirely to 
differences in cell number, and not in cell size, the number of dividing cells 
in all cases was reduced to the proper proportion for a common constant 
area of one square millimeter. This thus avoided error due to observation 
of roots of different sizes. This care was taken by Kellicott (14), but was 
omitted by Karsten (12 and 13). In all cases the area observed contained 
practically all of the dividing cells. 
Investigation 
Elongation 
Pisum sativum. Seeds of two varieties, viz., wrinkled (gradus), and 
smooth (No. I White Field of D. M. Ferry & Co.), were allowed to ger- 
minate, and when the radicles had attained a length of 50-70 mm. obser- 
vations began. All observations were made in a dark room and at constant 
temperatures, so that the results obtained could not have been influenced 
by environmental changes of temperature and illumination. (In all the 
following plant and curve numbers it has been thought best to reproduce 
here the numbers as they actually occur in the original data). Space will 
permit the reproduction of but few of the mass of figures and curves upon 
which these results are based. Table i shows a representative set of elon- 
gation measurements; while in table 2 the times of maxima and minima 
of ten plants out of a total of 50 of this species studied are grouped. The 
other 40 are duplicates of one or other of those given in this table. 
A study of curves 193 and 194 (figures in table i) shows that elongation is 
rhythmic or oscillatory in nature, three waves of elongation occurring in 
the 24-hour period. Elongation is least rapid at 1-3 P.M., rises to a 
maximum at 5-7 P.M., with other maxima at 11 P.M. to i A.M., and 5-7 
A.M., and minima at 9 P.M. and 3-5 A.M. These plants were of the 
smooth-seeded variety. Curve 174 again shows three waves of elongation; 
here, however, the maxima occur at 11 A.M., 9 P.M., and 5 A.M., and the 
minima at 7 P.M., i A.M., and 7 A.M. Curve 160 also shows three waves, 
with maxima at i P.M., 11 P.M., and 5 A.M., and minima at 11 A.M., 
9 P.M., and 3 A.M. Comparison of these curves seems to show little uni- 
formity. They are, however, not comparable for two reasons: (i) the 
first two are obtained from plants of the smooth-seeded variety and the 
latter two are from those of the wrinkled-seeded variety; (2) germination^ 
m the case of the first two was begun at 9 A.M., in no. 174 it was begun at 
8 P.M., and in no. 160 at 6 P.M. In order to make no. 174 comparable, 
with respect to time after initiation of activity, to plants started at 9 A.M., 
it will be necessary to move the entire curve (no. 174) backward ii hours 
or forward 13 hours; similarly, no. 160 will have to be moved backward 9 
2 In all cases throughout this paper the time stated for beginning of germination is the 
time when seeds were placed in the germinating chambers. 
