In most plants, the stem serves as a support for the leaves which act as solar collectors to produce food for the plant. Stem and leaf are tightly integrated together into the shoot system. Selective pressure in certain plant groups has resulted in modified stems that serve a number of different functions including food storage and defense. In some plants (cacti are examples), the stem is the primary photosynthetc organ and the leaves are very reduced. These modifications are represented inthis collection.
Link to entire set of stem images
The Actively Growing Shoot Tip:
As the apical meristem of the shoot produces new cells they become organized into one of the three primary meristematic tissues (protoderm, ground meristem, procambium). Also below the apical meristem different regions become organized into leaf primordia and bud primordia. Because of the tight integration of leaf and stem, stem anatomy is a bit more complex than that of the root. Strands of vascular tissue in the stem diverge into developing leaves. As they do so they leave behind an area of parenchyma tissue called a leaf gap. As presented earlier this is one of the defining characters of megaphylls (remember the leaves we are considering in these anatomy exercises are fundamentally different from those found in the lycophytes! - microphylls are not even homologous to megaphylls).
Link to views of longitudinal section of a shoot tip Coleus
Cross Section of Herbaceous Dicot: Pay particular attention to the vascular cambium consisting of both fascicular and interfascicular cambia. These two meristematic areas are integrated to form one continuous cylinder of dividing cells.
Link to views of whole Medicago stem cross section
Link to detailed view of Medicago stem cross section
Link to view of fascicular cambium of Medicago stem cross section
Link to view of interfascicular cambium of Medicago stem cross section
Link to view of vascular cambium in Coleus stem cross section
Cross Sections of a Monocot Stem: The Zea (maize) stem cross section, like that of Medicago, consists of ground tissue surrounded by epidermis. Vascular bundles are embedded within the ground tissue. Note however, that the vascular bundles are not organized into a well defined ring, but are scattered through the ground tissue. Hence, the ground tissue is not divided into pith, cortex, and pith rays. In maize we simply use the more general term, ground tissue to refer to these areas of parenchyma. Further, in monocots, the vascular bundles are closed: That is there is no area of cambium between the primary xylem and primary phloem in the mature stem. Hence secondary growth does not occur in Zea. This arrangement of tissues is typical of the monocots.
Link to view of a cross section of Zea (maize) stem
Modified stems
Rhizomes Link to view of Iris Tubers Link to view of Potato Bulbs Link to view of Onion Corms Link to view of Gladiolus Tendrils Link to view of Grape Stolons Link to view of Valesnaria Thorns Link to view of Hawthorne Cladophylls Link to view of Ruscus