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RAY C. FRIESNER 
is out of the question, since this work was done in a dark room and the 
temperature was kept constant, except in a few cases, to within one degree. 
It seems quite clear, also, that it is not due to heredity, in the case of 
seedlings, as Semon (32) and Karsten (12) believed, since it has been shown 
by a number of earlier investigators that plants placed in continuous dark- 
ness and uniform temperatures gradually lose the periodicity which they 
had exhibited when exposed to the alternation of darkness and light. Now 
it would be expected that these rhythms would show some relation to the 
normal changes of night and day, even though the experimental plants 
were not so exposed, if the rhythms were due to the hereditary persistence 
of such effects upon the parent plants. It has been shown, however, in the 
case of Pisum sativum seedlings, that these rhythms have no relation to 
time of day, but rather that they depend, for the precise time of their 
appearance, upon the time of day when metabolic activity is initiated. 
It was at first thought that the rhythm might be due, in the case of ger- 
minating bulbs, to the persistence of a habit acquired by the bulb, while the 
bulb was itself growing and so exposed to the alternation of darkness and 
light, and the subsequent transfer of this habit to the growing parts. This 
is also disproved, sinc^e roots grown from seeds, in the case of Allium Cepa, 
exhibited the same rhythms as those grown from bulbs. That the rhythms 
of elongation and cell division may have a relation to the diurnal rhythms in 
atmospheric pressure and electrical potential is also out of the question, 
since it has been shown that the time of the waves in elongation and cell 
division depends upon the time of the initiation of metabolic activity, and 
that they vary according to the time when germination is begun, regardless 
of atmospheric conditions. Stoppel (34) found a relation existing between 
curves for sleep movements of plants and electrical potential of the atmos- 
phere. 
The two processes, growth and cell division, must necessarily go hand in 
hand as two of the vital activities of germinating seedlings. Just what the 
precise relation between them is, is not so definitely known, though it is 
quite evident that a certain size of the cell must be attained before cell 
division ensues, since cells from corresponding parts of different individuals 
of the same species vary but little in size. In a comparison of the curves 
for elongation and cell division it is seen that a general reciprocal relation 
exists between these two processes whereby there is a slowing-up in the rate 
of elongation at the time when there is the largest number of cells undergoing 
mitosis. The fact that the processes of elongation and cell division show 
such a reciprocal relation to each other within the individual cell is not so 
difficult to understand, since there is probably not enough energy available 
to perrait both processes to go on at their maximum at the same time. 
It is to be recalled, however, that the zone of most extensive elongation in 
the root is not the same as the zone of mitotic activity (practically all mitoses 
occur within a zone bounded by the growing point and an imaginary line 
