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 is the middle layer of a leaf, which contains both palisade and spongy cells. The palisade layer of the mesophyll contains lots of chloroplasts to aid in photosynthesis. Discover more information on leaf structure from ascience teacher in this free video on science and nature.