75 



The first glance at the map shows that drug plants are very 

 unevenly distributed over the earth. It is not surprising that 

 they are scarce or absent in arctic regions and deserts, and in 

 other sparsely settled regions where there are few persons who 

 can identify and gather them. On the other hand, there is a 

 marked concentration of them in many mountainous regions. 

 This may be mostly because mountain regions generally retain 

 much of their original wild flora, and most medicinal plants 

 which may have originally inhabited fertile plains have given 

 way to cultivated crops. Another possibility is that the soil 

 has something to do with it. For some reason not understood, 

 medicinal plants seem to be rather partial to climax vegetation 

 with abundant humus, and scarce in acid soils (there are few or 

 none among the bryophytes, and in such acid-loving families 

 as the Cyperaceae, Juncaceae, Orchidaceae, Hypericaceae and 

 Ericaceae), and perhaps also in alkaline soils (preferred by such 

 families as the Chenopodiaceae, Cactaceae, Onagraceae, Borra- 

 ginaceae and Ambrosiaceae). If they really avoid alkaline soils 

 that may explain why they are much more numerous in the east- 

 ern than in the western United States. Mountains on the whole 

 seem to have soils neither acid nor alkaline, but approximately 

 neutral. 



If we interpret the tropics mathematically as that portion 

 of the earth within 23| degrees of the equator, 159 of the drug 

 plants mapped by Dr. Newcomb come from the North Tem- 

 perate zone, 59 from the tropics, and only 5 from the South 

 Temperate zone. Onlya few are common to temperate and trop- 

 ical regions. Dividing them by continents and smaller divi- 

 sions, we find that Canada has 17, the eastern United States 88, 

 western United States 14, Mexico and Central America 13, the 

 West Indies 11, South America 24, Europe 69, western Asia 24, 

 eastern Asia 40, Africa 29, and Australia and Polynesia 5. This 

 grouping of course involves more duplication than the zonal 

 one, for several species are common to different continents, or 

 native in one and introduced or cultivated in another. Of those 

 in the eastern United States, 62 are pretty certainly native, 

 16 are usually weeds, and 10 cultivated. Information is lacking 

 as to the status of those in other countries, but they are prob- 

 ably mostly native also; for it is not usually profitable to cul- 

 tivate a plant for medicinal purposes as long as the same species 



