Cosmos stem. Darkfield illuminated polarised light micrograph of a cross section through the outer part of the stem of a Cosmos plant (Cosmos sp.). This section shows several vascular bundles composed of xylem tissue which transports water, and phloem tissue which transports the products of photosynthesis. At the top is the epidermis with hair-like outgrowths called trichomes. Magnification: x100 when printed 10 centimetres wide.