Apical meristem, water and plant height

​Corn shoot apical meristem is genetically controlled to switch from producing new leaf and cells to the terminal male flowers of the tassel.  The main environmental factor influencing this switch in temperate zone corn is heat energy. Earlier maturing corn requires less heat to trigger this change in apical meristem products, allowing corn to mature in short seasons far from the tropical environments of corn’s origin. 
 
Plant height is determined by the number of cells produced by cell division at the apical meristem before switching to producing the cells that becomes the tassel and the elongation of the cells.  Elongation of the stem cells is enhanced by water pressure applied to the young cells before maturing with less flexible cell walls. Thus, water availability to the roots, root volume and transport of water to the expanding cells in upper plant also affects the eventual plant height.
 
Corn planted later than normal in temperate zones, accumulating heat units quicker than usual, produce fewer stalk cells because apical meristem is induced to produce tassel cells quicker. If water availability for cell expansion is less than optimum, the result of these two factors will be shorter plants than usual for a hybrid.