We have continued our study of the alkaloids of the roots of T. simplex L. The chloroform fraction of the mixture of bases was treated with acetone. The soluble part was chromatographed on a column of alumina, and from fractions 5-6 of the chloroform eluate were isolated golden orange crystals with mp 263°-285 °C, identical with thalicmidin. The phenolic fraction of the ethereal part of the mixed bases was dissolved in methanol, and white prismatic crystals of an optically inactive base C₂₀H₂₁NO₅ with mp 261°-263 °C (methanol) were obtained. The base is sparingly soluble in all organic solvents and in water; it dissolves in aqueous alkali and contains N-methyl, methoxy, and methylenedioxy groups. Its IR spectrum has absorption bands at 3640 cm⁻¹ (OH), 2900, 1240, 1130 (OCH₃), 2860 (N--CH₃), 1640 (C=O), 1040, 980 (CH₂O₂), 1615, 1580, and 1505 cm⁻¹ (stretching vibrations of an aromatic ring). UV spectrum: λmax 288 nm (log ε 3.95). The substance obtained proved to be new, and we have called it thalictricine. The mass spectrum of the alkaloid (MKh-1303 instrument, 40V, 0.4 mA, 135 °C) has peaks with m/e 335 (M⁺), 269, 207, 206 (the principal peak), 192, and 180. The features of the mass spectrum of the base agree with the data given for alkaloids of the cryptopine type. These properties of thalictricine show that it belongs to the alkaloids of the cryptopine type. The methylation of thalictricine with an ethereal solution of diazomethane gave a base with mp 164°-165 °C (acetone), the UV, IR, and NMR spectra of which were identical with those of β-allocryptopine. Since the properties of thalictricine differ from those of hunnemanine, the only possible structure remaining for it was determined.