A DID system can be used for fax and voice mail as well as for live voice connections. Compared to regular PBX service, DID saves the cost of a switchboard operator, calls go through faster, and callers feel they are calling a person rather than a company.
Key Concepts: In dicotyledonous leaves there are two types of mesophyll cells, palisade mesophyll and spongy mesophyll. Palisade mesophyll cells form a layer beneath the upper epidermis whereas spongy mesophyll cells are internal to the lower epidermis.
The vascular tissue system is composed of two different types of tissues: xylem and phloem. Although both xylem and phloem form a continuous tissue system throughout the plant body, the two tissues have different functions.ylem: The Water-Conducting Vascular Tissue. Xylem is a complex tissue composed of several different cell types. This tissue includes parenchyma cells, fibers, and two cell types specializing in water and mineral transport: tracheids and vessel members.