Fig. 136. Longitudinal section

Gallery: 
Fig. 136. Longitudinal section

(parallel with diameter) of one side of a stem of Lobelia inflata.
a, epidermis; p, parenchyma; b, medullary ray of wood; c, tracheae; d, pith; (magnified 300 diameters.)

This image is from Lobelia in the Drugs and Medicines of North America.