seedlings in the high-N regime, RWR of seedlings in the medium-N regime, and root biomass of seedlings in the low-N regime. First-year seedlings typically have high mortality rates, drought being the principal cause, with roots having been unable to develop enough to maintain contact with soil sufficiently moist to prevent the development of lethal seedling water stress. Somewhat paradoxically, however, Eis (1967a) observed that on both mineral and litter seedbeds, seedling mortality was greater in moist habitats (alluvium and Aralia–Dryopteris) than in dry habitats (Cornus–Moss). He commented that in dry habitats after the first growing season surviving seedlings appeared to have a much better chance of continued survival than those in moist or wet habitats, in which frost heave and competition from lesser vegetation became major factors in later years. The annual mortality documented by Eis (1967a) is instructive. Pests and diseases Seedlings are particularly vulnerable to attack by pests and diseases and can consequently experience high mortality rates. Pests and diseases which are especially damaging to seedlings include damping off, cutworms, slugs and snails. Transplanting Seedlings are generally transplanted when the first pair of true leaves appear. A shade may be provided if the area is arid or hot. A commercially available vitamin hormone concentrate may be used to avoid transplant shock which may contain thiamine hydrochloride, 1-Naphthaleneacetic acid and indole butyric acid. Images See also Plant propagation Potting soil References Bibliography P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): Biology of Plants, 7th Edition, W.H. Freeman and Company Publishers, New York, Plant morphology Plant reproduction