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RAY C. FRIESNER 
III and 112, out of a total of 14 different plants studied, are given on 
Plate XXIV. In these, also, three waves of elongation occur in the 24-hour 
period. 
Zea everta. For this study the White Rice (D. M. Ferry & Co.) variety 
was used. A single curve is shown on Plate XXIV for elongation. Too 
little work was done on this species to warrant definite conclusions. The 
curve, 102, shows two waves of elongation in the 24-hour period. 
Summary for Elongation. Summarizing briefly in regard to elongation, 
we find that (i) elongation in all plants studied proceeds in a wave-like 
fashion, two to four waves being exhibited in the 24-hour period; (2) there 
is more or less variation among the various individuals of the same species 
in regard to the precise time of day of the occurrence of maxima and minima, 
though these can be arranged into definite groups which show very little 
overlapping of time (see tables 2-6) ; (3) it is indicated, though not definitely 
proven, in the case of Pisum, that the precise time of the occurrence of 
maxima and minima depends upon the time when germination was begun, 
and shows no relation to the actual time of day. This latter point will be 
taken up and definitely proven in connection with rhythms in cell division. 
This fact, if true, might also account for a great deal of the variation jn 
elongation curves of plants of the same species placed in the germinating 
chambers at the same time, since it is possible that some of the seeds may 
have coats that are more permeable to water than others, and hence the 
precise time of initiation of metabolic activity would vary slightly. 
Cell Division 
Pisum sativum. For this work root tips from both the wrinkled-seeded 
and smooth-seeded varieties of peas were used. Curve 2 (figures in table 7) 
shows results obtained from a study of the wrinkled variety. Seeds were 
placed in germinating pots at 9 A.M. at a temperature of 25° C. and allowed 
to germinate for 72 hours. The radicles had attained a length of 20-50 
mm. when killing and fixing began. It will be seen that three waves of 
cell division occur in the period of 24 hours. The three maxima come at 
I P.M., 5 P.M., and 5 A.M.; and the minima come at 11 A.M., 3 P.M., and 
9 P.M. The two maxima coming at 5 P.M. and 5 A.M. are about equal 
in extent. It will be noticed throughout the curves that follow that those 
waves in the various curves from roots of the same variety of seed which 
are coordinate in regard to time of appearance, are not always of the same 
amplitude. Kellicott (14) found similar results in Podophyllum peltatum. 
A study of the figures from which this curve is drawn (table 7) shows remark- 
able uniformity of the different roots for the same hour. Only at 5 and 
II A.M. do any appreciable differences occur, and then they are of such a 
nature that they do not affect the character of the curve. Curve 27 shows 
results from a similar study of the smooth-seeded variety. These seeds 
