1. Smith P. A. 1991. Environmental factors influencing the germination of horehound (Marrubium vulgare L.). B. Ag. Sc. thesis. La Trobe University. Bundoora, Victoria, Australia.
2. Letters following this symbol are a WSSA-approved computer code from Composite List of Weeds, Revised 1989. Available from WSSA, 1508 West University Ave., Champaign, IL 61821-3133.
3. (PEG mol wt 8000), Sigma, St Louis MO, USA.