Plant defense against herbivory which differ from one another in both functional groups, and in basic carbon skeletons. Monoterpenoids, continuing 2 isoprene units, are volatile essential oils such as citronella, limonene, menthol, camphor, and pinene. Diterpenoids, 4 isoprene units, are widely distributed in latex and resins, and can be quite toxic. Diterpenes are responsible for making "Rhododendron" leaves poisonous. Plant steroids and sterols are also produced from terpenoid precursors, including vitamin D, glycosides (such as digitalis) and saponins (which lyse red blood cells of herbivores). Phenolics, sometimes called "phenols", consist of an aromatic 6-carbon ring bonded to a hydroxy group. Some phenols have antiseptic
Plant as rayon and acetate derived from plant cellulose. Thread used to sew cloth likewise comes in large part from cotton. Thousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to historic gardens, national parks, rainforests, forests with colorful autumn leaves, and festivals such as Japan's and America's cherry blossom festivals. While some gardens are planted with food crops, many are planted for aesthetic, ornamental, or conservation purposes. Arboretums