Taxonomic Position of the Alkaloids in Plants

Since the greater majority of plants still remain to be examined, the taxonomic distribution of alkaloids cannot be fixed with any certainty, and their total number and occurrence can only be guessed. About one thousand are now known, the structures of many of them being still undetermined (179). The chemistry of the flora of only a few regions of the world has been intensively studied (Australia Webb (180) Siberia Sokolov (181) ). It is estimated that 10% to 20% of all plants contain alkaloids, but such estimates are uncertain to the extent that our analytical methods often fail to detect traces. Improved methods have led to the finding of nicotine in tomatoes (182) and of alkaloids in 

The existence of larger quantities of alkaloids in plants depends not only upon the plant s capacity to synthesize them but also upon its capacity to tolerate them. The widespread occurrence of nicotine has often been noted, but it frequently is present only in traces (Lycoper-sicon, Atropa, Lycopodium, Equisetum, Asclepias). When tomato or 

A remarkable example of tolerance to a considerable accumulation of nicotine is that of Zinnia elegans Jacq. (Compositae), which surprisingly grows well when grafted upon a tobacco root. Strangely enough, it also contains nicotine when grown on its own roots (186). 

In the AmaryUidaceae the alkaloids seem to be confined to the subfamily Amaryllidoidae. Though the structural types are not uniform they seem to be confined to these monocotyledons with one remarkable exception, namely, the phenolic cocculine present in the Caucasian variety of CocctdMS laurifoUus DC. (Menispermaceae). This base, which appears to be absent from the East Asiatic varieties of the same species, apparently has the same ring skeleton as has lycorine, which is remotely related to the isoquinolines so common in the Dicotyledonae (193), 

Our knowledge of alkaloids in animals is scant. The so-called protoalkaloids (biogenic amines and their derivatives) are widespread in lower animals (194, 195), and the parallelism between plant and animal metabolism is extensive. Betaines, methylated purines (e.g., paraxan-thine (VI) ), derivatives of histidine (spinacine (VII) of the shark), and kynurenic acid (VIII) are not rare in animals. The animal alkaloids, with the exception of samandarine (Vol. V, p. 321), are characterized as weak bases this is perhaps of importance for their excretion. 

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