We have information from several sources:
Skullcap: Potential Medicinal Crop—Nirmal Joshee, Thomas S. Patrick, Rao S. Mentreddy, and Anand K Yadav
Sievers, A.F. 1930. The Herb Hunters Guide. Misc. Publ. No. 77. USDA, Washington DC.
Chinese Medicinal Herbs: Opportunities for Domestic Production—Lyle E. Craker and Jean Giblette