A striking variability in physiological and morphological characters occurs in many grass species of importance in grasslands cultivation .
As early as 1912, WITTE (12) reported the multiformity of timothy, cocksfoot, meadow fescue and tall oat grass . He not only found early and late forms in these species, but also observed differences in tillering, leaf position, leafiness and size, number and growth direction of the culms . Susceptibility to rust also appeared to vary, while in a later publication (13) he reported differences in drought resistance and persistency.
HESSING (5) investigated the variability in the ryegrasses and established three main types in his material, viz . V-shaped, U-shaped and prostrate plants . There were also many intermediate forms .
GREGOR and SANSOME (4), in the case of timothy, classified the plants according to growth-form and arranged them into the following division I . Prostrate : Stems prostrate, panicles lying on, or slightly raised above the ground . 2 . Decumbent : Stems decumbent, only distal internodes erect or ascending . 3 . Ascending : Peripheral stems decumbent-ascending, central stems sharply ascending but not truly erect. 4 . Erect : Stems perpendicular, except for lower internodes of peripheral stems .