Poa pratensis L., the common Kentucky Blue grass, is universally recognized by taxonomists as an extremely variable species. Many different strains are included within the species, and although American botanists do not generally recognise them as being sufficiently distinct to warrant their segregation from pratensis they are conspicuously present. Basic information on their variability, inheritance, and methods of reproduction would not only make it possible to classify the various strains more efficiently but it would allow us to use the species to best advantage for pasturage, turf, etc. It would also indicate what improvements might be expected by breeding for superior strains and the methods to be followed in making such improvements. In this investigation an attempt has been made to correlate data from morphological, cytological, and genetical studies in an effort to arrive at a clearer understanding of the behavior of the species.