Diurnal periodicity of somatic mitosis in the root-tips of eleven crop plants were investigated by the writer under the cooperation of seven students of our laboratory. The plants included in this investigation were Ozyza sativa L., Hordeum vulgare L., Triticum vulgare Vill., T. spelta L., T. monococcum L., Secale cereale L., Phaseolus angularis Wight, Ph. vulgaris L., Cannabis sativa L., Solanum tuberosum L. and Vicia Faba L.
The materials were collected from about one-month old plants transplanted into pots from the field one week before the experiment commenced. Root-tips of approximately the same size were fixed at 1- or 2-hour intervals throughout a 24-hour period on June 17-18, 1939. The number of nuclear divisions was counted for each of the samples as to be seen in Tables 1 and 2, and these data produce 11 curves as in Figures I-XI.
It is of interest to note that:
1) Main periods of nuclear division of most plants are a little past 0:30 AM as well as 0:30 PM.
2) Though some differences in the nature of the periodicity-curves are found among the plant materials used, two main dividing periods are distinct in all plants except Vicia.
3) Legumes and potato show a fairly distinct periodicity while hemp and some of the cereals show the secondary dividing periods beside the primary one, the monococcum wheat and rye showing no apparent periodicity.
The data represented in Tables 1 and 2 and in Figures I-XI will be a good help to us in the cytological investigation as well as in the experiment using chemical or physical agents to affect chromosomes or nuclear divisions.
