Hint: Hydrophytes are aquatic plants which may be floating or fully submerged in water. Submerged hydrophytes are not in contact with an environment other than water. Stomata are minute pores generally present on leaf epidermis.
Submerged hydrophytes are further of two types- rooted submerged hydrophytes and free-floating submerged hydrophytes. Rooted submerged hydrophytes are sessile and the roots only provide anchorage. E.g. Vallisneria. Stomata is absent in submerged hydrophytes because they live in a water-abundant area from which they derive all their nutrients. The requirement of gas exchange is fulfilled by the water which diffuses inside their body by osmosis.
Some general characteristics of hydrophytes are:
Roots: It is reduced or entirely absent. The roots that develop in Pistia, a free-floating hydrophyte, are only for balance. Nutrients are absorbed from all over the body. Roots play a minimal role in water absorption. Also, in place of root caps, root packets or root sheath.
Leaves: Floating leaves are present in partly submerged plants. Their upper epidermis has stomata and a layer of wax for its protection. They are feathery or long-ribbon in submerged plants for providing minimum resistance to the flow of water. A thin layer of the cuticle is present because the need to conserve water considerably decreases.
Stems: Aerenchyma or large air sacs are present to maintain the buoyancy of floating plants. It helps in easy diffusion of gases in the parts which are not exposed to the air.
So, the correct answer is ‘Nowhere on the plant’.
Note: Stomata are specialized epidermal structures whose primary function is the gaseous exchange between the plant’s internal tissues and the atmosphere. Loss of water in the form of water vapours also takes place in the process of stomatal transpiration. A stomatal apparatus consists of a stoma, bordered by two guard cells. Two or three subsidiary cells surround guard cells.