After the cavity has formed, the meristem (a region of plant tissue, found chiefly at the growing tips of roots and shoots and in the cambium, consisting of actively dividing cells forming new tissue) that is responsible for elongation is activated and the blade starts to elongate. During this period, smaller vascular bundles and connections between them are formed, internal structures such as epidermis(the outer layer of cells covering an organism,), mesophyll(the inner tissue (parenchyma) of a leaf, containing many chloroplasts.) and stomata(any of the minute pores in the epidermis of the leaf or stem of a plant, forming a slit of variable width that allows movement of gases in and out of the inter cellular spaces.) are also formed.
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