1.Karyological investigations of some twenty-four species in theLolium-Festucagroup were made as a preliminary to meiotic studies of selected species and hybrids. Comparative studies were made on relative length and arm ratio of all the chromosomes in the various species. The chromosomes with secondary constrictions were classified into sixteen types and designated as A.B,C,……J.2.In theLoliumspecies, which were all diploid, three inbreeding species,L. temulentum, L. remotum, L. loliaceumand four outbreeding species,L. multiflorum, L. westerwoldicum, L. rigidumandL. perennewere studied.(a)These studies confirmed that the basic karyotype was similar in the two groups and all the species had three pairs of satellited chromosomes. However, the two groups could be differentiated clearly on the basis of a difference in the position of the secondary constriction in chromosome 1.(b)Significant differences in relative chromosome length and arm ratio between corresponding chromosomes of different species were found.(c)There appeared to be more variability among the outbreeding species in respect of the various chromosome characters than in the inbreeding species.(d)It is concluded that many chromosome rearrangements have occurred in the differentiation of the various species but gene mutations must also have been involved.3.InFestucaseventeen species and six populations of tall fescue belonging to the sectionsOvinae, Bovinae, Scariosae, Montanae, Sub-bulbosaeandVariaewere studied.(a)All the diploid species differed in their karyotypes both with respect to relative length and arm ratio and the satellited chromosomes were distinct in the different species.(b)Karyotypes ofF. arundinaceavar.glaucescens(2n = 28) indicated similarities of some of its satellited chromosomes with those ofF. pratensis(2n = 14) andF. Mairei(2n = 28). In addition, similarities were also discerned betweenglaucescensand two other forms ofF. arundinacea(2n = 42,70). This indicated the phylogenetic relationship of these forms.(c)The tetraploid form ofF. spadiceaincluded some of the satellited chromosomes of its diploid form. Similar relationships were found between satellited chromosomes of the hexaploid forms ofF. amplaandF. rubrawith their octoploid forms respectively.4.Special attention was given to the karyotypic analysis of one indigenous and six exotic populations ofF. arundinacea(2n = 42). There was positive evidence of chromosomal differentiation between the populations.(a)The indigenous population had four satellited pairs whereas introduced ones had five to eight pairs. In addition diversity with regard to the size and shape of the satellites of different populations were also found. This variation was also observed with regard to arm ratio and relative length.(b)Chromosomal repatterning as a result of segmental inter-change, inversion and deletion must have played some significant role in the differentiation of tall fescue.5.Such karyotypic variations were also found in other species includingF. Mairei, glaucescens, arundinacea(2n = 70). Apparently chromosomal repatterning is well spread and possibly perpetuated by vegetative reproduction.6.The following general conclusions were also drawn:(a)The separate status accorded to the two generaLolium-Festucais supported.(b)In the evolutionary process there was no change in the basic chromosome number for the species in this group and there was evidence to support the view that the two genera had a common origin. Compared with the diploids the polyploids were of relatively recent origin.(c)From a study of chromosome asymmetry in the different species it was possible to evaluate the evolutionary trends in the genusFestucaand to show the significant part played by polyploidy in speciation.