Marques, Renata Pereira, et al. “Densities Straw and Luminosity Conditions on Seed Germination on Seed Germination of Euhphorbia Heterophylla”. Semina: Ciências Agrárias, vol. 33, no. 3, June 2012, pp. 867-72, doi:10.5433/1679-0359.2012v33n3p867.