All the above forms of cells and many more unite in certain definite relations to one another, forming a tissue (fig. 9). Most flowering plants, Ferns, Lycopods, and Selaginellas have representatives of various forms of cells, wood fibres, and vessels in their tissues, and are spoken of as fibro-vascular plants, and constitute the most highly developed members of the vegetable kingdom. A mushroom is not a fibro-vascular plant, as it is made up entirely of branching threads of thin-walled cells.

Uses Of Different Cells

The thickened outer cells of leaves and young stems are of a protective nature, so far as the cuticle is concerned, while the interior is thickened to impart strength. Wood fibres give rigidity to the stems of herbaceous plants and in a greater degree to trees, which have the greatest number of them; and they, in conjunction with the continuous tubes or vessels, serve for the rapid conveyance of liquids, containing ingredients of plant food, as well as elaborated food being carried to the points of growth or to be stored. The laticiferous tissue is more obscure, but some of the contents are of the nature of stored food. Some cells are set apart entirely for the purpose of marrying and reproducing the plant. The other cells have their respective duties, and have neither time nor opportunity for this. [J. F.]

Cut illustrating various tissues.

Fig. 9. - Cut illustrating various tissues. To the left Spiral Vessels, followed by long Conducting Cells. These are succeeded by Cellular Tissue or Parenchyma. In some of the square cells are Crystals of Oxalate of Lime. In the longer cells are groups of Needle-like Crystals called Raphides. To the extreme right are Pitted Cells.