Baumgartner, José Geraldo, et al. “Effects of Calcium and Or Boron Deficiency on the Peduncle of Sunflower Inflorescence”. Pesquisa Agropecuaria Brasileira, vol. 21, no. 7, Apr. 2014, pp. 747-55, doi:10.1590/S1678-3921.pab1986.v21.14883.