Research was done on the length regularities of leaves, which are determinate organs, in the Poaceae family species Lolium multiflorum, Festuca pratensis and ×Festulolium braunii. It was found that the first leaves of the shoots were shorter than those of further leaf ranks along the shoot (l1V2>V3>V4). We suggest that a shoot with more leaves, as physiologically older, more differentiated system accumulates resources and allocates them for regulation, which secures its higher stability, and consequently – lower variation of subsequent leaves. These leaves are just the ones that can be used in comparative studies.
Keywords: Lolium multiflorum, Festuca pratensis, Festulolium braunii, determinate growth, growth rate, total physiological age.