Xylem cells in the vascular system from the roots to the leaves is the main tube that allows water and minerals to be moved from roots to leaves. A major portion of the xylem, tracheids, are dead cells at maturity that have strong thick walls providing the strength to withstand strong water pressures but have small pores to allow flow into surrounding cells. Also, part of the xylem tissue, are living parenchyma that allow movement of water and minerals to other cells. These cells accumulate potassium ions to be distributed into mesophyll of leaves. Xylem parenchyma cells accumulate starches in the corn stalk pith areas, to be later moved thru the phloem vessels to the developing kernels after pollination.
Tracheid cells in the xylem do not have end walls allowing them to form a tube. Water pressure from water entering the root cells to the movement of water to leaves where a portion of it evaporates through open stomata openings, causing transpiration pull. This push and pull causes a constant flow of water through the tubes of the xylem.
Phloem cells provide the transport of sugar and protein molecules up and down the plants. Xylem cells provide the flow of water and minerals up the plant. Movement in the phloem occurs via living membranes and requires energy. Movement of the water from roots upward does not require energy but simply removal of water through stomata and tendency of water molecules to adhere to other water molecules (cohesion). Thick xylem tracheid walls form the tube to contain the force.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.