Studies on the effect on root growth of continued rotation about a horizontal axis

Abstract

An attempt has been made to discover whether or not the growth rate of roots rotated about a horizontal axis is affected by the speed at which the rotation occurs. The method entailed a double selection of the roots to ensure that all the roots used in each experiment were straight and of equal initial length. Pea roots were used and the seedlings were intact throughout the experiment. The roots were held horizontally in jars which were supported in horizontal cradles. These cradles were attached to rotary spindles driven electrically and connected by driving chain to a geared klinostat so that their rotary speeds could be varied. The whole apparatus was enclosed in a box from which the light was excluded. The roots were photographed every half hour through a vertical slit in the wall of the box, a light being switched on momentarily inside while the exposure was made. The negatives were developed and the roots at successive half hourly intervals were measured from these negatives with a travelling microscope. The increases in length and hence the growth rates were calculable. This was repeated at various speeds. Graphs of growth rate against time have been plotted. Correlation coefficients have been calculated for growth rate on time and regression lines have been drawn. Some statistical analyses have also been done. There appears to be no well defined effect of speed of rotation on growth rate although rotated roots seemed to have a lower growth rate than vertical non-rotated roots and, in general, the slower the speed of rotation the lower the growth rate. Time does seem to affect the growth rate trend and appears to have most effect when the growth rate is generally high and also when the speed of rotation is high. N.B. Figures 1-8 will be found in the text and Figures 9 - 25 will be found in the Appendix.