The Unilateral Effeet of Gravity upon the Growth in Thickness of Abelmoschus gultins-textilis, KAGAWA

1) The growth in thickness, the changes of tissues, and the distribution of starch and oxidising enzymes seen in the horizontal hypocotyl and stem of A.gultins-textilis which is still in the early stage of growth, have been compared with those seen in the vertical one, and the unilatera effect of the force of gravitation acting upon the plant has been studied.2) The growth in thickness at the horizontal part in the axis of A.gultins-textilis is more accelerated than that at the corresponding part of the vertical axis as a whole. In the hypocotyl, both of the cortex and xylem grow more in thickness in the upper side than in the lower, while, in the stem, the xylem grows more in thickness in the upper side and, on the contrary, the cortex in the lower side. This is due tothe fact that the stem is stilll growing in elongation. In other words, by keeping it in the horizontal position, the growth in elongation at the lower bide, and thus, the upward growth of the stem, is forcibly suppressed. So that, in the stem or hypocotyl, which has finished its growth in elongation, both of the cortex and xylem grow more in thickness in the upper side, than in the lower. And, in this case, light has little effect on the mode of the growth in thickness of the axis kept in a horizontal positon. Therefore, it may lie said that A. gultins-textilis in the stage of growth in thickess belongs to the epitrophical type under the unilateral effect of gravity acting transversally to its longitudinal axis.3) Through the horizontal treatment, the development and Iignification of fibrous cells of A. guliins-textilis are accelerated in the upper side and retarded in the lower. In the upper side, the lines of fibrous bundles are gathered to form a group of a narrow pyramidal shape and moreover, each line of fibrous bundles leans toward the flanks, while in the lower side, each line of fibrous bundles is almost independent or even if some of the' lines of fibrous bundles are gathered to form a group, they merely present a trapezoid shape. This is due to the difference of oppression caused by the fact that the division and growth of cells, occupying the inner parts of cortex, are the most vigorous at the zenith of the upper part and those decrease gradually with transition to both flanks. In the upper side, moreover, as the development of fibrous tissues does not keep pace with that of cortex, there arise unevenness at the outer surface and crevices due to the destruction of tissues at the point between the cortex and the top of the primary fibrous bundle. Such changes disappear gradually with the transition to the lower side from the flanks.4) The cells in the outer layers in tlie cortex of the horizontal stem as well as hypocotyl become flat in the upper side and somewhat spherical in the lower side. The collenchyma of the stem are promoted in their development, especially, at the upper side, while in the lowor, they lose their chaiacteristic features and coiue to show larger intercellular spaces. The parenchymatous cells in the inner part of the cortex become also flat and narrow in the upper side, but those in the lower become larger and spherical and their intercellular spaces become larger.5) The structures of tissues of the vertical stem and hypocotyl are similar to those of tlie flanks of the horizontal ones respectively.6) In the xylem of the vertical stem or hypocotyl, the parts, such as medullary rays, etc., in which cells have thin cellulose walls and the paits which contain the vessels and consist of cells with thick lignified walls, alternate radially with each other, while in the xylem or hypocotyl treated horizontally, the greater part of the upper side is made up of larger cells with thin cellulose walls and thus the vessels as well as the lignified cells develop a little in semi-circular zones along the periphery of the xylem. On the contrary, the walls of almost all the xylem cells in the lower side are lignified and become thicker, but among those lignified cells, the cells with thin cellulose walls may be formed to a small extent in semi-circular zones. So that, it may de concluded that the lignification of the xylem cells are retarded in the upper side and accelerated in the lower side of the horizontal axis, respectively.7) The activity of cambium in the upper side of the horizontal axis is neaiiy the same with that of the vertical one, and it seems that the cambium in the lower side of the horizontal axis is much inferior to them in activity.8) In the horizontal stem as well as hypocotyl the reactions of oxidising enzymes are stronger in the upper side and those of starch in the Iower.9) The differences of inner structures between the upper side and lower of the axis are clearly shown where they have ceased to grow in elongation, even if they have been left horizontally without any compulsion.10) It has been affirmed that the part of the stem appiicated with α-naphthalene acetic acid in lanolin (2 mgs, of α-naplthalene acetic acid per gr. of lanolin) shows the similar phenomenon to the upper side of the stem horizontally treated, but this only concerms with the swelling-out of the cortex and distribution of starch.11) The morphological and physiological differences arising between the upper side and lower in the same axis horizontally bent, are considered to be the expression of a change of polarity due to the unequal distribution of the growth hormones and enzymes by the unilateral effect of gravity acting upon the axis transversally