Iris. Fig. 1.—Diagram of cross-section of rhizome

Fig. 1.—Diagram of cross-section of rhizome of Iris versicolor, the section passing through near the base of one of the joints;
a, a vasal-bundle in the cortex;
b, cylinder-sheath;
c, a vasal-bundle in the central cylinder. Magnification, 6 diameters.

This image is from Structure of Iris. in the American Journal of Pharmacy, 1895.