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.
On the top and bottom are the cuticle layer and the epidermal cells. In the middle, between the epidermis cells on the top and bottom, are the mesophyll cells where the chloroplasts live. On the bottom only, in most plants, are the stomates which let carbon dioxide in and oxygen out. More on the Leaf Section : Mesophyll Cells No, it's not a Mess of Phils. It's a mesophyll. The chloroplasts, where photosynthesis occurs, are in the mesophyll cells. There are two kinds of mesophyll cells in our typical leaf. The ones you see in the leaf section above, packed close together, are in the palisade parenchyma region (I can't say it either - that's biologists for you).