Organ-2 It is inefficient for one cell to perform a multitude of functions. Consequently, cell specialization evolved. The cells on the bottom could have been specialized for water absorption . They might have had a thin Cuticle and could have hair -like projections called Rhizoids .
Rhizoids are like root hairs and they are specialized for the absorption of water .
They also anchor the thallus to the substrate. This would constitute a Tissue called Epidermis . The upper layer could loose its photosynthetic abilities and become more specialized for water retention . It would constitute another layer of Epidermal Tissue . The Chlorenchyma is thus embedded within the two specialized Epidermal layers.