Micrographs of trichomes
Another feature of bean leaves is the presence of trichomes on both the top (adaxial) and the bottom (abaxial) leaflet surface.
It is said that historically bean leaves were used to remove bed bugs. Individuals would brush the bedding with the leaves and the bugs would become hooked on the trichomes. The leaves were then destroyed (Szyndler et al., 2013).
Below are pictures of those hooked trichomes.
Figure 41. Trichomes on the upper surface (adaxial) of a bean leaflet. On red kidney bean leaves there are numerous trichomes, almost 20 per 1.00 mm2. Credit: E.T. Paparozzi
Figure 42. Trichomes on the bean leaflet lower surface (abaxial). Red kidney bean leaves have trichomes on both sides of the leaflets. Credit: E.T. Paparozzi
Figure 43. Trichomes on the midrib (adaxial). The midrib of the middle leaflet of the third trifoliate has straight and hooked trichomes. Credit: E.T. Paparozzi
Figure 44. SEM close-up of hooked trichomes. A closer view of the hooked trichomes which are about 1 µm wide. If you stroke the leaf gently, you can feel them! Credit: E.T. Paparozzi
Figure 45. The tip of a bean leaflet hooked trichome. The pointed tip is approximately 0.1 µm wide. Perfect for impaling small insects (ex. bed bugs are 4-7 mm in diameter). Credit: E.T. Paparozzi
These trichomes are not only found on a red kidney bean plant’s leaflet, but also on all the stems and other places. Take a closer look at Figs. 2, 5, 9 and so on.