7] TYPES AND AREAS OF NATURAL DISTRIBUTIONS 187 



Saxifrage, which is also alpine {cf. Fig. 49). Indeed, most circum- 

 polar plants are at the same time circumboreal, though the converse 

 is by no means true. The boreal and austral zones lie next to the 

 arctic and antarctic ones, and seem best considered as extending to 

 the border of the subtropics. Examples of groups having such 

 distributions are shown in Fig. 47, the circumboreal being the genus 

 Ribes (Currants and Gooseberries) and the circumaustral the southern 

 species of Danthonia (Poverty-grasses and Wild Oat-grasses). 



Fig. 48. — Map showing pantropic distribution of the Palm family (Palmae). 



(After Good.) 



(4) Pantropic — extending practically throughout the tropics and 

 subtropics, or at least widespread in the tropical regions of Asia, 

 Africa, and America. A fine example is the Palm family (Palmae), 

 as indicated in Fig. 48. Most, but by no means all, pantropic 

 species appear to have been introduced by Man through much of 

 their range. 



It may be noted in the above that when a very wide view is main- 

 tained, mere outliers can be overlooked and even oceans practically 

 ignored, distributions across them being considered continuous. 

 Moreover, as we proceed from the poles to the tropics and the 

 distances involved expand, there is a tendency for fewer and fewer 

 minor taxa to be circumglobal. Indeed, in the tropics, subtropics, 

 and adjacent warm-temperate regions, it is not uncommon for whole 

 genera and even larger groups to be limited to closely adjacent or 

 even single land-masses. 



