Vaucheria is a siphonaceous and coenocytic alga . It is aseptate but septa are formed at the time of formation of reproductive structures. The wall of the filament is thin and is made up of an outer layer of pectic substances and an inner layer of cellulosic substances. The asexual reproduction in Vaucheria occurs by means of Aplanospores, Synzoospores ,and akinetes

A Meristem is a localized region of the cell which are dividing actively. There are various theories of the shoot apical Meristem. Apical Theory: It was proposed by Nageli. A single tetrahedral apical cell is the structural and functional unit of the cell . It controls all the growth processes of the cell. It is found in algae, bryophytes and pteridophytes. Histogen Theory: It was proposed by Hanstein. There are three Histogenic layers. Dermatogen which gives rise to epidermis. Periblem is destined to form the cortex. Pleurome forms the vascular cylinder. Tunica Corpus Theory : The peripheral zone consisting of one or more layers of regularly arranged cells is called as tunica and the cells surrounded by tunica is called as corpus. Histogenic layer theory: This theory was proposed by Dermen. There are three Histogenic layers . LI , LII and LIII layers