"Petroleum plants". Morton JF. Science. 1976 Nov 12;194(4266):678. doi: 10.1126/science.194.4266.678-b. PMID: 17832519
"Petroleum plants". Clawson M. Science. 1976 Nov 12;194(4266):678. doi: 10.1126/science.194.4266.678-a. PMID: 17832520