By systematic fractionation of the alkaloid-rich pH 7 fraction from G. vellosii three new alkaloids, viz., vellosimine, vellosiminol, and geissolosimine, have been isolated. Vellosomine and vellosiminol are indoles, and by n.m.r. studies and comparison with known alkaloids, have been shown to have structures I and III, respectively. Geissolosimine (formerly called D22) is a dimeric alkaloid and is cleaved by acid to the indole, vellosimine, and the indoline, geissoschizoline. From this cleavage reaction, its reconstitution from vellosimine and geissoschizcline, and its n.m.r. spectrum, geissolosimine has been assigned structure VII. © 1962, American Chemical Society. All rights reserved.