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Mesenchymal stromal cells were first isolated from the bone marrow, where they serve as a component of the tissue microenvironment. These cells provide a physical support for the other cells of the tissue; i.e., the hemopoietic cell lineage, and further participate in the formation of bone structures. Most importantly, stromal cells regulate the growth and differentiation of hemopoietic stem cells. The mesenchyme is not specific to the bone marrow: such cells are found body-wide, and serve similar regulatory functions. By the same token, the mesenchymal stroma contributes to tumor formation by providing regulatory signals. In addition, the stromal cells themselves may undergo transformation, and subsequently form tumors. This chapter discusses these two major aspects of stromal cell involvement in the tumorigenic process. [ABSTRACT FROM AUTHOR]

How vainly men themselves amaze To win the palm, the oak, or bays; And their uncessant labours see Crown'd from some single herb or tree, Whose short and narrow verged shade Does prudently their toils upbraid; While all flowers and all trees do close To weave the garlands of repose. The common aims of plants and animals are the conversion of energy to their own purposes and the perpetuation of their species. All energy in the solar system ultimately comes from the Sun as light emission, and organisms that can use this source directly belong to one of the autotrophic groups, which are independent of outside sources of organic substances. These direct solar energy converters, or phototrophs, are almost exclusively plants, the rare exceptions being found among the bacteria. An example of this latter esoteric group is Halobacterium halobium. But not all plants are autotrophic. A major division, or phylum, of the plant kingdom are the mycophyta, or fungi, which include mushrooms, moulds and yeasts. These heterotrophs are all either saprophytes, obtaining nutriment in solution from the decaying tissues of plants or animals, or parasites. The latter group are important agents of disease, mainly in other plants but occasionally in animals. We will not be concerned here with such plants, and neither will we consider all phototrophic plants. The algae, which are simple photosynthetic plants, were formerly classified as belonging to a single taxonomic division. [ABSTRACT FROM AUTHOR]