Phloem-Food conducting Tissue in vascular plants

primary cells are called sieve elements (because there are clusters of pores at the ends of cells through which adjacent protoplasts are connected)
cells are living at maturity, but the nucleus and tonoplast are broken down
sieve cells have sieve areas with uniform, narrow pores
sieve-tube elements may have larger pores on some walls than on othersà sieve plate
companion cells are specialized parenchyma cells associated with sieve-tube elements; may play a role in delivery of substances to sieve-tube elements
albuminous cells—found in gymnosperms
Think of xylem and phloem as long pipes or tubes that extend from the roots all the way throughout the plant to the top leaves, even in tall trees! In order for tall trees to prevent wilting, water must be moved continuously from the roots to replace water being lost through transpiration.