Out of the vast array of species in the plant kingdom - variously estimated at from 200,000 to 800,000 - a few have been employed in primitive societies for millennia to induce visual, auditory, tactile, and other hallucinations Because of their unearthly effects that often defy description, they have usually been considered sacred and have played central roles as sacraments in aboriginal religions (Schultes, 1969c). Scientific interest in hallucinogenic agents has recently been intense, partly because of the hope of finding potentially valuable drugs for use in experimental or even therapeutic psychiatry and also for employment as possible tools in an explanation of the biochemical origins of mental abnormalities (Hoffer &. Osmond, 1967) . While psychoactive species are widely scattered throughout the plant world, they appear to be concentrated more or less amongst the fungi and the angiosperms. The bacteria, algae, lichens, bryophytes, ferns, and gymnosperms seem to be notably poor or lacking in species with hallucinogenic properties (Schultes, 1969-70). These hallucinogenic properties can be ascribed, likewise, to only a few kinds of organic constituents, which may be conveniently divided into two broad groups: nitrogenous and non-nitrogenous compounds (Der Manderosian, 1967a; Farnsworth, 1968, 1969; A. Hofmann, 1961a, 1968; W. 1. Taylor, 1966; Usdin &. Efron, 1967). See Figure 1 for basic chemical skeletons. The nitrogenous compounds play by far the greater role and comprise, for the most part, alkaloids or related substances, the majority of which are, or may be biogenetically derived from, the indolic amino acid tryptophan . They may be classified into the following groups: 1. beta-carbolines; 2. ergolines; 3. indoles; 4. isoquinolines; 5. isoxazoles; 6. p-phenylethylamines; 7. quinolizidines; 8. tropanes; 9. tryptamines. Non-nitrogenous compounds, which are the active principles in at least two well known hallucinogens include: 1. dibenzopyrans; and 2. phenylpropenes; other compounds, such as catechols and alcohols, may occasionally play a role . In the study of hallucinogenic plants , two considerations must be borne in mind. One consideration reminds us that there are some of these psychoactive plants used in primitive societies for which the active chemical principles are as yet not known. The other emphasizes that man undoubtedly has utilized only a few of the species that actually do possess hallucinogenic principles: we are, as yet, far from knowing how many plants are endowed with psychotomimetic constituents, but there are certainly many more than the few employed by man as hallucinogens (Schultes, 1967a). While almost all hallucinogenic compounds are of vegetal origin, a few may be wholly or partly synthetic. The potent hallucinogen, lysergic acid diethylamide (LSD), although very closely allied chemically to the naturally occurring ergolines, has not been found in the plant kingdom.