DERIVATION OF THE FLORA AND FAUNA 34I 



S. Pacific, particularly between Australia and Samoa in lat. io° to 25°; (3) Eastern 

 N. Pacific off the west coast of Mexico and Central America. Occasionally tropical 

 storms develop near Hawaii and over Australia. The normal course of (i) is WNW, 

 recurring NE, and of (2) WSW, recurring SE. To what extent plant distribution 

 runs parallel to cyclone tracks has, as far as I am aware, not been investigated. 

 As ViSHER says, most of the cyclones originate over the sea "well out in the 

 ocean" (p. 87). They hit many of the Polynesian islands, and possibly collect 

 diaspores on one and deliver them on another, but a frequent dispersal of species 

 in this way does not appear very probable. I wonder whether there is in Hawaii, 

 with its 90 % endemics, a single flowering plant likely to have been borne there 

 by a cyclonic storm. ViSHER is, however, opposed to land connections in the 

 Pacific, with one exception: "it is known that Australia was formerly connected 

 with Asia by way of the East Indies and New Caledonia" (j^J. 77). With regard 

 to Polynesia he points to the west-east hurricanes and their colonizing power. 

 Sea carriage also comes into the picture, violent cloudbursts may accompany the 

 storm, brooks are transformed into swift rivers carrying plant material, tree trunks 

 and soil, forming rafts, which are washed out into the ocean. 



A recent paper by Bergeron (j^^) gives a somewhat different aspect. His 

 map shows the two areas in the Pacific north and south of the equator, where 

 hurricanes arise, and how they move. The Hawaiian islands lie, as a rule, outside 

 the tracks. The direction north of the equator is NW or WNW all through the 

 hurricane belt, and there is no sign of an easterly direction enabling plants and 

 animals to be carried all over Polynesia as far north and east as Hawaii, as ViSllER 

 supposed. South of the equator the trend is S and SE; the east of the Pacific 

 is not reached and Juan Fernandez lies, in longitude as well as in latitude, away 

 from any cyclonic belt. 



It has often been stated that spore-plants, theoretically at least, have much 

 greater facilities to colonize on long distances, but it has been shown that in 

 reality their capacity is more limited than was formerly assumed. 



COPELAND (68. 165-166) expressed his opinion on the diffusion of fern spores: 



Fern spores are carried across water by the wind — ten miles of water is no barrier 

 at all to their spread. One hundred miles may be one hundred times as great a barrier, 

 because the spores must hit a target, a suitable place to germinate and grow. Still, 

 ferns spread readily across seas this wide. A thousand miles makes the obstacle again 

 one hundred times as great ... the limited viability of the spores, the chance of falling 

 or being washed out of the air, and the chance of very different climate at such dis- 

 tance, increase it materially. Ferns rarely jump a thousand miles of ocean. Still a number 

 of species are believed to have crossed the south Atlantic, and I believe that three 

 genera, Plagiogyria, Coniogramtne and Loxogra?nme, have flown the north Pacific from 

 Japan to Mexico, each in one single instance. It is not exacdy impossible that direct 

 colonization has occurred between Chile, New Zealand, Tasmania, the Cape, and Tristan 

 da Cunha. 



It should be mentioned that CllRlST (59), with his unique knowledge of the 

 distribution of ferns, pointed to the insignificance of spore dispersal as an 

 explanation of the origin of widely disjunct areas. 



