Staining of invertase activity in the root apex of maize (A), wheat (B) and melon (C). (A) – the longitudinal section of the root tip, in which the root cap was detached, (B, C) – the whole root tips. The dashed line on each root indicates the boundary between the meristem and the elongation zone. The boundary between the root zones was determined by morphometric analysis. Bar – 500 µm.