Happy birthday to Vera Rubin! The pioneering astronomer turns 86 today.
It All Stems From Stems.
Xylem and Phloem tissues are found together in vascular bundles in the stems of plants and trees. The xylem transports water and soluble mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis. Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. The transport taking place in the xylem is passive. Surface tension caused by the evaporation of water to the atmosphere pulls more water and minerals up from the roots like a straw.
Unlike xylem, which is composed mainly dead cells, the phloem is composed of still living cells that transport sap. The sap is a water-based solution, but rich in sugars made by the photosynthetic areas. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs. During the plant’s growth period, usually during the spring, storage organs such as the roots are sugar sources, and the plant’s many growing areas are sugar sinks. The movement in phloem is multi-directional, whereas, in xylem cells, it is uni-directional (upward).
All images above © Dr. Keith Wheeler / Science Source