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A NUMBER of investigators have noticed cyclic variations in the average numberof mitoses in different tissues of plants and animals corresponding to theL 24 hour daily cycle; in these reports it is assumed that variation in light isthe critical factor determining this periodicity. A number of plants have been studied.Karsten (i) found that in Spirogyra a maximum mitotic activity appeared about midnight; in Allium, Kellicott (2) observed two maxima: a primary one at 11:00 P.M.,and a secondary rise at 1:00 P.M. On the other hand, Stälfelt (3) noted that mitoticactivity in roots of Picum sedaticum occurs at 9 to 11 A.M. Furthermore, Berinsohn(4) found that Allium root tips contain more karyokinetic figures after a period ofexposure to darkness than after a similar exposure to light. Similarly in animals, the reports of several investigators show a marked differenceas to the time at which maximum mitotic activity occurs.
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Herman T. Blumenthal (1940) studied this question.
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