A Study of the Root System of Barley

Abstract

Summary The lengths of branched and unbranched axis, the density of branching, and the change in length of laterals along the axis (called the root profile) were determined on roots of Maris Badger and Proctor barley (Hordemn vulgare L.) grown in water culture under complete nutrient supply and deficiencies of potassium and phosphorus. The most striking observations were (a) 50–75% reductions in the length of unbranched axis caused by nutrient deficiency, (b) marked curvilinearity in the profile under all nutrient treatments, and (c) high dependency on the form of the profile on variety and nutrition.

A Model of the Extension and Branching of a Seminal Root of Barley, and Its Use in Studying Relations Between Root Dimensions I. the Model

“…Evidence of this has been found not only in intact plants but also in defoliated plants (Evans 1971) and ones mutilated by removal of the tips of the root axes (Hackett 1971).…”

“…The morphological terms used in this paper are applied in accordance with the definitions given by Hackett (1968Hackett ( , 1971, with the exception that, following Barley (1970), the classes of laterals are now termed first-order, second-order, and thirdorder instead of primary, secondary. and tertiary.…”

“…Relations between only the number and length of root members therefore needed to be considered. Neither of these simplifications was possible when considering mutilated roots (Hackett 1971).…”

“…The development of the root system of barley (Hordeum vulgare L.) and other graminaceous species proceeds in such a manner that relations between the total number, length, surface area, and volume of the root members remain approximately constant during the vegetative stage of growth (Shearer 1968;Hackett 1969Hackett , 1971Evans 1970Evans , 1971. Evidence of this has been found not only in intact plants but also in defoliated plants (Evans 1971) and ones mutilated by removal of the tips of the root axes (Hackett 1971).…”

A model of the Extension and Branching of a Seminal Root of Barley, and Its Use in Studying Relations Between Root Dimensions II. Results and Inferences From Manipulation of the Model

“…Because published data imply that ba and qf vary within quite narrow limits (Weaver, Kramer, and Reed 1924;May, Chapman, and Aspinall 1965;Hackett and Bartlett 1971), and because b f and qs were found from manipulation of the model to have small effects on 1 when vf was at or below the standard value, it can be suggested that the constancy of 1 in intact roots is due primarily to the existence of ceilings to va, vI> and Vs, and secondarily to the characteristic expression of tf, t s, ba, and qf' Within these constraints, wide variation in root form is obviously possible, and most of it would be expected to give roughly constant values of 1. Thus it can be perceived why the phenomenon has been observed in experiments where the relevant data have been collected, and it can be expected that it will be commonly observed in the future.…”