THE EFFECT OF CENTRIFUGAL FORCE ON ROOT‐TIPS OF PISUM SATIVUM AT VARIOUS TEMPERATURES

Abstract

FROM INVESTIGATIONS on centrifuged plant cels various workers have drawn conclusions as to the structure, viscosity, and specific gravity of the several cell elements by noting the ease with which the elements move in the surrounding medium. The degree of movement depends not only upon the viscosity of the medium through which a particle moves but also upon the difference in specific gravity between the particle and the medium. By varying the viscosity it should be possible to determine the relative specific gravity of the various cell elements, provided the specific gravity and the viscosity do not change in the same direction under the same stimulus. F. and G. Weber (1917), Pantin (1924), and Lambers (1925) have demonstrated that, within limits, the viscosity of protoplasm decreases as the temperature increases. Mottier (1899) was the first investigator to study the effect of centrifugal force upon the living contents of the cell. He centrifuged trichomes of Tradescantia, Urtica, Momordica, and Cucurbita; root-tips of Zea Mays, Phaseolus vulgaris, Allium cepa, and Vicia faba as well as various algae and mosses. Mottier reported that in the trichomes and root-tip cells the nucleus, cytoplasm, and cytoplasmic inclusions were forced as a dense mass into the lower end of the cell while the vacuoles were compelled to occupy the opposite end of the cell. Mottier noted that in the embryonic cells of the root-tips, the nucleolus occupied a normal position after centrifuging. However, in older cells, the nucleolus usually was in contact with the nuclear membrane toward which the force was directed, and in a few cells the nucleolus was thrust through the nuclear membrane. An identical centrifugal force, however, did not eject the nucleoli from the nuclei of the various trichome cells. During cell division, early prophase stages showed but a slight displacement of the spireme. In later stages, in some cells the mitotic figures occupied an oblique position against the basal wall after being centrifuged. When this occurred, slight distortions were noted in the spindle fibers, but the chromosome groups were not thrown together. There appears to be but one published account of the behavior of mitochondria in centrifuged cells. Faure-Fremiet (1913), working with centrifuged eggs of Ascaris meqalocephala, reports that when the cytoplasm is not highly viscous the mitochondria may be centrifuged out, demonstrating that their specific gravity exceeds that of the cytoplasm. At 350C. four minutes were required for the mitochondria to