STUDIES IN THE BEHAVIOUR OF THE RHIZOME OF AGROPTRON REPENS(L.) BEAUV.

Abstract

(1) The mode of growth of the rhizomatous grass Agropyron repens (Couch Grass) is described. The plant produces new rhizomes in the spring from basal lateral buds. The tip of each rhizome grows in a horizontal direction below the soil surface during the spring and summer before erecting in the autumn to form a primary aerial shoot. This shoot develops into a mature plant during the following year.By sampling a mature stand of Agropyron plants it is shown that the development of the primary shoot is marked by the production of a succession of leaves, internodes and lateral shoots which vary in length or form according to a well‐defined pattern. Usually 7 lateral buds at the base of the primary shoot grow out in the spring to form lateral shoots. Of these, the four most basal ones develop into rhizomes and the remainder into tillers. Plants growing in open communities develop differently in that secondary tillers and rhizomes are formed during the first growing season. Rhizome growth is not related to flower formation.(2) From experiments it is found that:(a) Rhizome growth can be induced during the winter under warm greenhouse conditions by increasing the intensity of illumination of the plants to within the range 500–2000 ft. candles.(b) No rhizome growth occurs under natural conditions when the illumination intensity is reduced to approximately 3 per cent of the noon summer value.(c) When rhizome growth is induced to begin approximately 4 weeks prematurely, then rhizome growth ceases in Mid‐July.(3) These results are discussed. It is concluded that rhizome growth is dependent upon the plant being brightly illuminated and that rhizome initiation in the spring is controlled by environmental factors, while rhizome cessation among plants in closed communities is most probably the result of the parent aerial shoots becoming senescent.The problem of the orientation of the rhizome and its depth adjustment in the soil will be considered in a later paper.The work described here was carried out in the University of Sheffield, England. The author is indebted to Professor A. R. Clapham for much invaluable advice and criticism. Grateful acknowledgment is made to the Department of Scientific and Industrial Research for a maintenance allowance which made this investigation possible.