One interesting feature of the vascular bundle sheath can be the presence of crytals which can be easily observed under polarized light. These are generally calcium oxalate and in the picture they are the white star-shaped bodies lined up along the vascular bundles of the stem. The crystals which are observed in these images are classified as rhomboid and are commonly found in stems and leaves. Note the distribution of the trichomes along the stem which are also nicely lit-up in these images.

Cotton stem median longitudinal section, 4x, polarized light, brightfield, Matt

Another interesting feature is the presence of buds and their impact upon the structure of the vascular bundles. Below are two views where the bud clearly affects the structure of the secondary vascular tissue. Note how both the annuli of the secondary phloem and xylem are distorted around the bud and that the usually blocky pith cells are elongated as well in the area subtending the bud.