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.
Mesophyll tissue is made up of parenchyma cells that lie between  the upper and lower epidermis layers of a leaf. The parenchyma  cells that make up this tissue are essentia â¦ l for photosynthesis in  plants. Joshua Florendo. 11 Contributions.