In DSM, nicotine dependence is included under the general definition of substance dependence.  The essential feature of Substance Dependence is a cluster of cognitive, behavioral, and physiologic symptoms indicating that the individual continues use of the substance despite significant substance-related problems.
The Best Materials to Cover your Greenhouse. 1  Glass: The traditional greenhouse covering, glass is the preferred material for permanence. 2  Film Plastic: Film plastic is one sixth to one tenth of the cost per square foot of a glass covered structure.
Cost... There surely is no cheaper means of acquiring a walk-in greenhouse than building a PVC greenhouse. The frame consists of nothing more than PVC pipe. The 'purlin' of the greenhouse in the photo above is simply strong twine running along the top center of the house and looped around each PVC bow. Some rebar stakes, a bit of lumber for framing the ends, the plastic covering â and thatâs it.