Plant cell the major classes of cells and tissues of roots, stems, leaves, flowers, and reproductive structures, each of which may be composed of several cell types. Parenchyma cells are living cells that have functions ranging from storage and support to photosynthesis (mesophyll cells) and phloem loading (transfer cells). Apart from the xylem and phloem in their vascular bundles, leaves are composed mainly of parenchyma cells. Some parenchyma cells, as in the epidermis, are specialized for light penetration and focusing or regulation of gas exchange, but others are among the least specialized cells in plant tissue, and may remain totipotent, capable of
Plant life-form plant functional type, which has recently replaced "life-form" in a narrow sense. Following, some relevant schemes. Based on plant habit: Humboldt described 19 (originally 16) "Hauptformen", named mostly after some characteristic genus or family: Based upon the duration of life and the height of the ligneous stem: Based on the place of the plant's growth-point (bud) during seasons with adverse conditions (cold seasons, dry seasons): Vegetation-forms: Main life-forms ("Grundformen") system: Growth-form system: Main groups of plant life forms: Following, other morphological, ecological, physiological or economic categorizations of plants. According to the general appearance (habit): According to leaf hardness, size and