Plant stems have a variety of functions, including photosynthesis, support, and movement of water and sugars throughout the plant.
Each picture shown below has a brief description underneath it. Scroll over the picture in order to see which type of cell is identified by the cursor.
For descriptions of all cell types and their functions, click here.
Stems consist of several layers. The outermost layer is the epidermis, covered by a cuticle. In many stems, there is a layer of collenchyma inside the epidermis, which helps provide structural support. Collenchyma cells are what make celery stringy. Several other tissues are found in stems, but their orientation differs among species. These include the cortex (parenchyma cells), vascular cylinder and pith (parenchyma cells). The term cortex usually refers to parenchyma cells towards the outside of the plant, while pith refers to the tissue in the center of the stem or root.
This picture shows a cross-section of a dicot stem. The genus name is Cucurbita. The xylem and phloem together make up the vascular bundles, which are continuous pipelines for movement of water and sugars throughout the plant. This particular genus has bicollateral vascular bundles, which means that phloem is found on both sides of the xylem. In many plants, this is not the case, as phloem is found on only one side of the xylem. Note that the parenchyma cells at the upper right corner have starch grains in them.
This shows a cross-section of Medicago (alfalfa) stem. Based on the arrangement of the vascular bundles, do you think this is a dicot or a monocot stem? (For a review of monocot and dicot characteristics, click here).