Stalk is also known as "millable cane". It develops from the bud of seed-cane. When seed-cane is planted, each bud may form a primary shoot.
From this shoot, secondary shoots called "tillers" may form from the underground buds on the primary shoot. In turn, additional tillers may form from the underground secondary shoot buds. The stalk consists of segments called joints.
Each joint is made up of a node and an internode. The node is where the leaf attaches to the stalk and where the buds and root primordia are found. A leaf scar can be found at the node when the leaf drops off the plant. The length and diameter of the joints vary widely with different varieties and growing conditions. The colors of the stalk seen at the internodes depend on the cane variety and environmental conditions.
For example, exposure of the internodes to the sun may result in a complete change of color. The same variety grown in different climates may exhibit different colors. All colors of the stalk derive from two basic pigments: the red color of anthocynin and the green of chlorophyll.
The ratio of the concentration of these two pigments produce colors from green to purple-red to red to almost black. Yellow stalks indicate a relative lack of these pigments. The surface of the internode, with the exception of the growth ring, is more or less covered by wax. The amount of wax is variety dependent.
The top of the stalk is relatively low in sucrose and therefore is of little value to the mill. The top 1/3 contains, however, many buds and a good supply of nutrients, which makes it valuable as seed cane for planting.
A cross section of an internode shows, from the outside to the center, the following tissues: epidermis, cortex or rind, and ground tissue with embedded vascular bundles. The cells of the rind are thick-walled and lignified. These cells help strengthen the stalk. More toward the center, the ground tissue contains the vascular bundles with the xylem and phloem.
Xylem tissue conducts water and its dissolved minerals upward from the roots, and phloem conductive tissue transports plant- manufactured nutrients and products, for the most part, downward toward the roots.
Two types of cracks are sometimes found on the surface of the stalk; harmless, small corky cracks, which are restricted to the epidermis, and growth cracks which may be deep and run the whole length of the internode.
Growth cracks are harmful since they allow increased water loss and expose the stalk to disease organisms and insects. Growth cracks are dependent on variety and growing conditions.