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RAY C. FRIESNER 
noon, with the minima at 8 A.M. and 4 P.M. Finally, in continual darkness 
the maxima came at 4 P.M. and 8 A.M. with the minima at midnight and 
noon. Two waves were found in all these curves. The work of Kellicott 
(14) also shows two waves in the curves for cell division in roots of Allium 
Cepa grown from bulbs and in moist sawdust. The maxima came at 1 1 P.M. 
and I P.M. and the minima at 3 P.M. and 7 A.M. It should be noted that 
in his curve I no figures are given for 5 A.M., and that in his curve II the 
curve rises from the "normal" 11 P.M. maximum to a much higher one at 
5 A.M. This point will be referred to again in connection with my own 
results. It should also be noted that a total difference of 13° C. appears 
between the highest and lowest temperatures, though there is apparently 
no direct relation to be noted in the curves between these temperature 
changes and changes in rate of cell division. Roots of Podophyllum peltatum 
also showed rhythms in their curve of cell division, though they were more 
numerous than in Allium. 
Karsten (12) studied cell-division in the root tips of Vicia faba and Zea 
Mays. The curve for Vicia faba showed marked maxima at 9 A.M. and 
9 P.M. with minima at 4 P.M. and 7 A.M., and a few minor variations. 
The curve for Zea Mays showed smaller oscillations throughout the entire 
24-hour period, though the curve is higher from 5 A.M. to 6 P.M. and lower 
from 6 P.M. to 5 A.M., the highest point being reached at 7 A.M. and the 
lowest at 9 P.M. These experiments were conducted in continuous dark- 
ness. 
Miscellaneous 
■ It is of interest and indirect bearing on the present paper to mention a 
few other cases in which either rhythm or a daily periodicity is found. 
Pfeffer (26) found nearly the same results in regard to sleep movements of 
leaves, viz., plants subjected either to constant illumination or to constant 
darkness lose their regular daily periodicity. In some cases autonomic 
waves are found under uniform conditions, and in others they are entirely 
absent. When present they show considerable variation both in different 
individuals and in different leaves of the same plant. Baranetzky (2) and 
Detmer (7) have shown that there is a single wave in the daily curve for root 
pressure. The maximum, while varying somewhat in different individuals, 
comes some time in the afternoon and the minimum about 12 hours later. 
In a recent paper, Romell (28) reports the same results from plants con- 
tinually lighted: ''Die Dauerlichtpflanzen, ohne Ausnahme, eine sehr 
ausgepragte Tagesperiodicitat in der Blutungskurve besassen." Hum- 
phreys (11) calls attention to the presence of two rnaxima and two minima 
in daily atmospheric pressure, and in electrical potential. Similarly, 
Dechevrens (6) reports, from observations in Jersey, the presence of a 
diurnal rhythm in electrical potential of the atmosphere. Kraus (15, 16) 
and Millardet (24) have shown that the daily periodicity of tissue tension 
is gradually lost when the plants are exposed to uniform conditions. Finally, 
