The examination of Calotropis gigantea (R.Br.) leaf anatomy yielded some interesting results about the plant's epidermal features. For example, numerous epidermal trichomes can be observed with the naked eye on both the upper and lower surfaces of the leaf. These trichomes are white, soft hairs that are relatively easy to remove.

However, upon closer inspection it was found that these epidermal trichomes are multicellular (Figure 1). There was no evidence of secretion and these are probably non-secretory hairs. A reasonably thick cuticle is apparent on the adaxial side of the leaf (Figure 1). Needs a Label.

Figure 1: Multicellular trichome on the adaxial side of the leaf. Note the thick cuticle to the right of the trichome.

It was also surprising to discover that although only cross sections were made, the sections rolled or curved slightly in such a way as to reveal stomata on both the upper and lower surfaces (Figures 2a and 2b). The stomata appeared to be located in the same plane as other epidermal cells. They were not recessed. Stomata appeard to be be the same for each side of the blade. Rhey appeared to have subsidiary cells but further work would be required to determine this.

Figure 2a. Adaxial epidermis with stomata.

Figure 2b. Abaxial epidermis with stomata.

Figure 3: Leaf mesophyll unstained

Microscopic examination of leaf blade cross sections revealed that the mesophyll is bifacial and consists of a highly organized palisade layer just under the adaxial epidermis and a spongy layer with many airspaces occupying the area just under the palisade layer and just above the abaxial epidermis (Figure 3). Small lateral veins can also be observed in Figure 3. Needs a Label. The chloroplasts are much more concentrated in the palisade layer of the mesophyll.

Figure 4: Leaf midrib with crossed polarizers

The anatomy of the midvien can be seen in Figures 4 and 5. Figure 4 was taken with crossed polarizers. Hereafter called full polarization. This method reveals the birefringent nature of the xylem which forms a crescent-like shape. There is only one large vascular bundle in the midrib. Other tissues in the midvein with thickened walls are found above and below the midvein. Label These are birefringent  due to a high degree of wall thickening.

Figure 5. Leaf midrib stained with Toluidine Blue

The midrib was stained with Toluidine Blue (Figure 5). This helps to resolve the vascular tissues with greater certainty. The xylem stains blue and can be seen have the same crescent-like form as seen in Figure 4. The phloem is clustered around the xylem and stained a pink-red color with Toluidine Blue.

Figures 6a and 6b show a greater magnification of  the midvein. Both images show the thick, highly organized nature of the xylem cell walls. However, the birefringence of the xylem cell walls can be seen in Figure 6b, which was taken under polarized light.

Figure 6a. Xylem tracheary elements in the unstained midvein xylem: Note the thick walls of the tracheary elements.

Figure 6b. Xylem tracheary elements in the unstained midvein photographed with crossed polarizers: Note the birefringence of the tracheary elements.

Figure 7a. Laticifers in leaf midvein

Figure 7b. Laticifers in leaf midvein with partially crossed polarizers.

During the course of this study unidentified brown spots were observed in the leaf. These were most evident in the Midrib, especially in the midvein (Figures 7a and 7b). These were later found to be laticifers, which produce the milky latex that is so common in this family.