340 



C. SKOTTSBERG 



venturadas. In this case it is not the question of identical species and rarely of 

 j^enera. It is not improbable that the secret of their origin and early history lies 

 hidden in the far soutii, but tiiis is all we can say. Hemslev (727. 66) when dis- 

 cussing the endemic Coni[)ositae of Saint Helena and Juan Fernandez said that 

 "wind seems at first to be the most probable agent"; still he doubted its efficiency. 

 In Setciiell's view storms seem to ofler more than a possibility in many in- 

 stances, particularly tropical cyclones and vertical thrombs able to carry even 

 lieavy diaspores to a great altitude. In another paper (218) he points out that 

 plant distribution in the Pacific has been from west to east against the prevailing 

 winds and currents and, in the case of Hawaii, has given much better results 

 than the expected east-west route; the "frequent cyclonic storms" are responsible 

 for this anomal}' together with adverse biotic factors, but I fail to see why they 

 shouldn't ofter the same difficulties for diaspores coming from the west. 



Andrews (^.615) paid s})ecial attention to the occurrence of scattered "Ant- 

 arctic " genera and species in and around the Pacific and combines their distri- 

 bution with the direction of ocean currents: 



In the South Pacific the westerly current sweeps by Australia, New Zealand, Tahiti, 

 and the whole of the west const of South America, where it is joined by the cold 

 uprising water along the South American coast. This gives rise to the north-moving 

 Peruvian C'urrent which sweeps by Juan Fernandez, Peru, Central America, and Mexico, 

 whence there is a detlection westerly toward the Hawaiian Islands and the tropics. 

 This knowledge of the general circulation within the Pacific appears to throw a flood 

 of light on the occurrence of the Australian, New Zealand and western South American 

 elements in the Hawaiian flora, such as... (2 5 genera are enumerated). The influence 

 of ocean currents is suggested i)articularly in the peculiar distribution oi Acaena, Gunnera, 

 Acrfcra, On-obolus, Sautalinn, Sophora, and so on. 



Juan hY-rnandez lies outside the Peruvian current, but also the outer island, Masa- 

 fuera, is reached by drift-wood. Its origin has not been investigated. 



A look at a current-chart shows that Andrews' reasoning has its weak 

 points; besides, I cannot see that the genera he mentions are thalassochorous. I 

 would recommend the reader to take a look at the many distribution maps pub- 

 lished in a paper read on the same occasion when Andrews presented his argu- 

 mentation ( iVeS). 



\\ ith regard to the cyclonic storms several authors have, as we have seen, 

 em[)hasized their j)r()minent role in the violent dispersal of both plants and ani- 

 mals; they are, in fact, considered to be the only imaginable force by which 

 larger objects are trans|)()rte(l, and it is useless to deny that such events have 

 taken j)lace and still take })lace, even if it is difficult to find definite proofs that 

 the transport did lead to the establishment of an immigrant from afar. Most 

 authors who have taken refuge in c>'clones have, however, expressed themselves 

 in general terms without a clear idea of the extension of the cyclonic belts and 

 the trend of the cyclones. 



In two j)apers \'lsiiER has summarized his studies on cyclonic storms in the 

 Pacific. Three chief centres of origin are distinguished [322): (i) Western N.Pacific, 

 originating some distance east of the Philippines in lat. 8° to 25°; (2) Western 



