Berhan Tewolde (PhD)Medhanie Ghebrehiwot2018-07-182023-11-092018-07-182023-11-091982-06http://etd.aau.edu.et/handle/123456789/9237Investigation for possible chemical interactions among some of the common grass species that grow in and around Addis Ababa was undertaken. The species used were the grasses Alldropogon abyssinicus R. Br. ex Fl:·esen, Hyparrhenia arrhenobasis (Hochst. ex. Steud.) Stapf, Pennisetum glabrum Steud., SnOl"ldenia polystachya (Fre san) Pi Ige1', E leusine jaegeri Pi Iger, &ragrosti8 tenuifolia (A. Rich) Steud. and a legume, ~!edicago polymorpha L. The effects of the extracts of the seven species on the seed germination and plumule and radicle growt'h of the same seven species shoW}d that ~. abyssinicus and ~. polystaohya were the most inhibitory followed by H. arrhenobasis and .!!!... jaegeri in that order. Extracts from!!!... tenuifolia, H. polymorpha and P. glabrum showed less inhibitory effects than the above species. See.d germination inhibition effect Was greatest on ~. polystachya and P. glabrum and that on E. jaegeri and H. arrhenobaaia '"aa the least. Auto-inhibition ,"as found to be as high as allo-inhibition. Extracts from all the species except!!!... tenuifolia ShO\fed auto-inhibitory effecta on germination and plumule growth and/or radicle grovlth. Different experiments Vlere carried out to detect the \fay of release of the inhibitory chemical(s) in ~. abyssinious. The results obtained from these experiments indicate that !. abyssinicus inhibits other speoies when decomposition of its dead .remains takes place and that the live plant doss not re lease any alle lopathic st'bstance into the soil mediumenGrassesThesis