Microscopy of a Ranunculus Stem
100x Magnification
The 100x view of this Ranunculus stem provides more detail to differentiate tissues. The epidermal cells with cuticle as waterproofing are more visible. These cells lack chloroplasts. Chloroplasts within outer cortical parenchyma cells are becoming visible. Remember, stems are commonly photosynthetic whereas roots typically are not. Each vascular bundle contains xylem to the inside and phloem to the outside. These two tissue types are just becoming visible below the sclerenchyma fiber caps of the vascular bundles. Light does not penetrate into deeper cell layers of stems so parenchyma cells located here lack chloroplasts. In many stems, these inner cells function as storage parenchyma.
200x Magnification
In moving to a 200x view, sclerenchyma type cells of xylem and fibers stand out against the thin-walled parenchyma cells of cortical and phloem tissues. A closer look also reveals some parenchyma cells resident within the xylem. Remember, when cells develop thick secondary walls as sclerenchyma types they lose ability to replicate. Parenchyma cells like these within the vascular tissues are called upon to produce new cells via mitotic cell divisions when needed.
400x Magnification
The 400x magnification is positioned over the vascular bundle to provide a closer examination of the typical tissue types. Sclerenchyma fibers, visible to the lower right, form a protective cap over the vascular bundles. Immediately above(internal to) the fibers are parenchyma cells of phloem. Just internal to the phloem cells(to upper left) are thick-walled cells of xylem. Notice how fibers are smaller in diameter with much thicker cell walls than those of the more open xylem. Both are sclerenchyma cell types but their different functions determine their structure. Narrow diameter fibers function in support and protection whereas more open xylem cells function in the transport of water and minerals.
1000x Magnification
The 1000x magnification allows a close look now at the interface between phloem and xylem within the vascular bundle. Contrast these two cell types and compare differences in the thickness of cell walls. Nuclei of companion cells are usually visible in the phloem. One is visible here! This higher magnification also allows a view of intercellular junctions and middle lamellae between xylem cells. Also, look for some pits!.
In this low magnification (40x) image of a Ranunculus stem, attributes of a dicot stem can be viewed. In contrast to a monocot stem with its randomly arranged vascular bundles, the dicot stem contains vascular bundles arranged in a concentric ring. This is somewhat similar to the arrangement of vascular tissues in a monocot root. Remember, roots contain endodermis! This epidermis appears thicker due to a cuticle or waterproofing layer. Just below the epidermis lie parenchyma cells of the cortex. Outermost parenchyma cells of the stem cortex can contain chloroplasts and be named chlorenchyma. Each vascular bundle is capped by sclerenchyma fibers. The deepest parenchyma cells of this stem fragmented during growth to produce the hollow pith area.
Note: To magnify this image, move your mouse to the right and let it rest on an icon for each desired magnification.
