During the past three decades the organic chemist has become in- creasingly used to take advantage of more and more complex instrumenta- tion and physical measurements in lieu of laborious, time-consuming and often ambiguous chemical transformations. Mass spectrometry is perhaps the most recent, most complex and most expensive addition to this field. In view of the astonishingly quick acceptance of nuclear magnetic reso- nance by the organic chemist it is, in retrospect, surprising that he has neglected mass spectrometry for such a long time. This can be explained, in part, by the complexity of the instrumentation and some technical shortcomings of the earlier commercially available instruments but, to an even greater extent, it reflects also the prejudices against a technique that was originally mainly used for quantitative gas analysis. The usefulness of mass spectrometry as a qualitative technique in organic chemistry rather than a tool for quantitative analysis was more and more recognized towards the end of the last decade. A rather spectacular development followed during the intervening few years to the point that now any reasonably well equipped modern organic laboratory is supplied with, or at least has access to, one or more mass spectrometers suitable for work on organic compounds. Within the realm of organic chemistry the technique has become much more important, if not indispensable, for the natural products chemist while its application to synthetic problems is much less pro- nounced.

In their monumental work "The Cactaceae", BRITTON and ROSE (I9) record 1235 species belonging to the three tribes which constitute the family of the Cacti. The actual number of the species must be con- siderably higher. Cacti occur frequently in tlie more arid and less accessible regions of the American Continent, nearly always within very narrow and definite borderlines. The habitat of a species is in many instances a single valley located in a remote, uninhabited region of the Cordillera. Thus the collection of flowering specimens fit for botanical identification is some- times extremely difficult. On the other hand, cacti are apt to develop individual variations in their characteristic morphological features, rendering the definition of a species difficult and often illusory. Specimens taken from their normal habitat to botanical gardens or arboreta often die, degenerate or stop flowering. Taking into account all these difficulties, it is not surprising to find considerable differences of opinion among botanists on the taxonomy of the cactaceae. A considerable number of species have not been well defined and in many cases different names have been given to the same species. The index of BRITTON and ROSE records not less than 7000 binomials.