The vegetative grass tillers

• The grass family all have in common a segmental structure called tillers which are made up of a chain of phytomeres in different stages of development.
• Each phytomere, after formation at the apical meristem or growing point goes through a lifecycle similar to that of its predecessor.
• By contrast, as grass phytomeres grow old and die, they are replaced by younger phytomers in an organized manner, such that the plant form, and often plant size as well, is maintained despite the appearance of new phytomers and loss of older one.
• This confers a capacity of replacement of tiller that die, and a protection of meristems from damage or loss by defoliation.
• A new phytomer, after differentiation just below the apical meristem, first forms a bulge to one side, the leaf primordium.
• The primordium develops over a period of time into a hood-shaped structure, enclosing the meristem to form a dormant branch meristem or bud in the axil of the leaf below.
• Next, the leaf elongates through cell division in a meristematic region itself divided into an upper band that later becomes the leaf ligule and a lower band which forms the leaf sheath.
• Leaf sheaths of successive leaves enclose each other, forming the pseudo stem.