The Inhibiting Effect of Dead Roots on the Growth of Bromegrass

N connection with another investigation, bromegrass, Brmus I inermis Leyss, and two other grass species were grown for 3 months in pure stands and in mixtures in sand watered with nutrient solutions. The total number of plants in each culture of the pure stands and mixtures was always the same. The nutrient solutions were identical but were replenished by the addition of the same amount of nutrient salts rather than changed during the course of the experiment. Under these conditions it, was noted that the greater the proportion of bromegrass plants in the stands the smaller the dry weight of these bromegrass plants. At the close of the experiment analyses of the nutrient solutions indicated that these decreased dry weights were not due to mineral deficiencies occurring in the solutions. This suggested the possibility that when bromegrass is grown a substance, or substances, inhibitory to its own growth accumulates in the substratum, which in the above experiment had accumulated in the unchanged nutrient solutions. It also seemed that such a substance could either be excreted from the living roots, liberated from the dead cells sloughed from the living roots, or formed by the decomposition of these dead cells. With these points in mind plants of bromegrass were grown in 2-gallon crocks filled with quartz sand with which 0, 7, and 2 5 grams, respectively, of oven-dried roots were thoroughly mixed. The seeds were planted in the sand on March 7 and the plants harvested on April 2 2 , 1941. The plants in all treatments were watered with a nutrient solution known to give good growth of bromegrass. The solutions were applied by the hand-operated system described by Withrow and Biebe1.l The dry weights of the plants in the various treatments are shown in Table I. Each value is the mean of 12 replications of I O plants each.