A stem is a collection of integrated tissues arranged as nodes and internodes. Nodes are regions where leaves attach to the stem. Internodes are the parts of the stem inbetween the nodes.
Stems support the leaves. Leaves are supported by a stem’s internal skeleton of collenchyma and schlerenchyma. turgor pressure in stems provides a hydrostatic skeleton that supports the young plant.
Stems produce the carbohydrates. Stems of some plants are photosynthetic. Although it is insignificant compared to those produced by the leaves, in plants such as cacti it accounts for most of the plants CO2 fixation.
Stems store materials. Parenchyma cells in stems store a large amount of starch and water. For example, water accounts for as much as 98% of weight in cacti syems.
Stems transport water and solutes between roots & leaves. Stems link leaves with the water and dissolved nutrients of the soil. The vascular sytems of stems maintains an aquatic environment in leaves and transports sugars and other solutes between leaves and roots.