314 Transactions. — Botany. 



for these facts by the action of oceanic currents alone, even if 

 in past time they were different in direction from those at 

 present existing. Moreover, the distribution of the Fucacece 

 and the Laminariea gives a character to the antarctic Algse 

 that seems to denote something more than dispersal from a 

 common centre. 



However, a full discussion of this question would involve 

 an investigation into the distribution of the seaweeds through- 

 out the southern ocean, and would lead me quite outside of 

 the scope of this paper. We have in ocean-currents no doubt 

 a vera causa, but what the limits of its action are would be a 

 very difficult matter to determine. The generally westerly 

 drift in the forties will no doubt go far to explain some of our 

 difficulties. It may possibly account for the presence of some 

 Fuegian forms in Tasmania and New Zealand, but not in 

 Australia ; and the trend of this current at the south of the 

 Cape may explain the absence of Fuegian plants there. In 

 speaking of D'Urvillcea utilis, Hooker says, "Though carried 

 by the currents along the ocean to the south of the Cape of 

 Good Hope (for it was collected in that meridian in the 51st 

 degree, floating in the open ocean), it does not appear to 

 inhabit or be cast upon the southern extremity of Africa."* 

 Such statements as these, in the absence of knowledge as to 

 the age of the species and of oceanic currents, can only be 

 looked upon as conjectures ; but, making every allowance for 

 their possible truth, there is still, I think, presumptive evidence 

 in the facts already given that other causes have been at work 

 in determining the present distribution of the iUgae in southern 

 oceanic islands. 



Whether species at present discontinuous may at one time 

 have been widespread we are not likely to be able to determine, 

 nor can we consider this as a means of explanation until 

 extraneous evidence has been brought forward to show that 

 areas at present widely separated were more closely connected 

 in the past. Such evidence is not altogether wanting. The 

 theories of Mr. A. E. Wallace! and Captain HuttonJ are well 

 known here, and I need scarcely refer to them further ; but 

 I should like to quote a short passage that may not be so well 

 known to New Zealand readers, from the "Botany of the 

 'Challenger' "§ : — 



" The now complete botanical researches for the present 

 work have brought to light some interesting facts, confirm- 

 ing generally the views enunciated by Darwin, Hooker, and 



* " Flora Antarctica," vol. ii., p. 455. 

 t" Island Life," 2nd ed., chap. xxii. 



{"New Zealand Journal of Science," vol. ii., p. 1 : " Origin of the 

 New Zealand Fauna and Flora." 



§ " Botany of the ' Challenger,' " vol. i., pp. 4, 5. 



