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.
Vascular tissue may be scattered in ground tissue or regularly arranged forming a ring. In the latter arrangement, ground tissue is differentiated into cortex (outer to vascular tissue) and pith (inner to vascular tissue). The ground tissue of leaves is called mesophyll, bound by upper and lower epidermis. TISSUE TYPES