304 EDMUND W. SINNOTT AND IRVING W. BAILEY 



That during its greatest extent, however, it was probably not a 

 continuous land bridge but more in the nature of a great archi- 

 pelago, presenting a barrier to most animal invaders but much more 

 easily crossed by plants, seems to be generally admitted. It is 

 worth our while to analyze the ancient "endemic" flora of this 

 antarctic continent and archipelago and to find, if we may, what 

 the climatic conditions were under which it flourished. It seems 

 to be a reasonably safe conclusion that all genera commonly desig- 

 nated as "antarctic," from their confinement to the temperate 

 regions of the Southern Hemisphere, were once inhabitants of Ant- 

 arctica. The writers have compiled a list of eighty-eight dicoty- 

 ledonous genera which have representatives in at least two of the 

 three main antarctic regions — New Zealand, Austraha, and tem- 

 perate South America — and which possess but very few species 

 outside these regions. This list may well be regarded as represent- 

 ative of the flora of Antarctica (except for the northern invaders) 

 before the advent of the cold period which drove the phanero- 

 gamic vegetation northward into South America and Australasia. 

 Of these eighty-eight genera only thirty-four, or 38 per cent, 

 are typically herbaceous. These few herbs are obviously unre- 

 lated to northern ones and seem clearly to have had an inde- 

 pendent origin in the antipodes in response to the refrigeration 

 of the climate. That they are not as ancient as the northern herbs 

 appears to be indicated by the fact that the annual type has not yet 

 been evolved among them. If the northern invasion which crossed 

 Antarctica did not enter it until the Pliocene (as seems probable), 

 no very extreme refrigeration could have taken place until the latter 

 part of that period, at any rate. The very high percentage of 

 woody plants in the original flora, however, seems to testify strongly 

 to the existence in Antarctica at no very ancient date of a climate 

 devoid of extreme cold. The refrigeration of this climate and the 

 evolution of its herbaceous vegetation, instead of being the slow 

 and gradual processes that they were in the Northern Hemisphere, 

 seem to have been much more rapid. The consequently scanty 

 number of herbs and the lack of time or space for very vigorous 

 competition among them doubtless explain why the antarctic 

 herbs are not as widespread and aggressive as their northern con- 

 geners. 



