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 inside of the leaf looks like this: Spongy mesophyll cells are not packed so tightly together, which allows carbon dioxide and oxygen to reach the palisade cells where they are needed in photosynthesis.Spongy mesophyll cells and guard cells (see below) also get some photosynthetic action.his tissue is called the mesophyll, meaning middle leaf, and comes in two flavors: the palisade mesophyll (sometimes called palisade parenchyma) and the spongy mesophyll. Most photosynthesis takes place in the palisade mesophyll, which is conveniently located at the top of the leaf just under the epidermis.