Studies of root function in Zea mays. II. Dimensions of the root system

Seminal roots of Zea mays were fixed, tied in a bundle with all branches parallel to the main stem, and embedded in Spurr's medium by a slow infusion method. The embedded root system was sectioned transversely at several points along its length. Two types of measurements were made on the sections. First, the number of root cross sections in each of several size classes, based upon root diameters, was determined so as to obtain the total length (per gram total weight) of root branches of a given diameter. Second, 12 root cross sections of various sizes were selected for further measurements. These included the cross sectional areas of the cortex, endodermis, stele, and xylem vessels, together with the circumferences of the cells and vessels in each region. From this information the total cell surface area, both outside and inside the Casparian strip, was calculated and used to express in absolute terms the various parameters measured previously.