312 Tra i mictions . — Bo tan y . 



overlooked even by a casual observer, so that their non-exist- 

 ence in southern Australia may be regarded as proved. Such 

 are Adenocystis lessonii, Lycluete danoinii, and Nitophyllum 

 multinerve. Why should these plants be found at such widely 

 intervening points, but not have crossed Bass Strait ? Why, 

 again, should five plants be confined to New Zealand and the 

 antarctic islands? And, lastly, why should only two of the 

 thirty-one reach South Africa? 



Of course, no matter what explanation be accepted, there 

 will always be difficulties and anomalies in the way of its 

 complete adoption. For example, Codium adherens has gene- 

 rally been regarded as a plant belonging to warmer seas. It 

 just reaches the south coast of England, and the coldness of 

 the waters of the Atlantic was believed to prevent it from 

 spreading northward. However, it occurs plentifully in New 

 Zealand, and the " Challenger " has shown that it is also 

 found at Kerguelen. Nevertheless it is wanting both at 

 the Cape and Australia. The genus Microcladia occurs on the 

 coasts of the Atlantic, California, New Zealand, and Ker- 

 guelen. As the species are small, it may, however, be yet 

 found in the intervening positions. 



There are at least six possible solutions of our difficulties : 

 (1) Further knowledge may fill in gaps at present existing, and 

 reduce apparent anomalies ; (2) dispersal may have taken 

 place by other methods than those already referred to ; or the 

 present distribution may be due — (3) to existing, or previously 

 existing, ocean-currents, (4) to the partial extinction of species 

 once widely spread, (5) to the former greater extension of 

 land-surface in the southern oceans, or (6) to some combina- 

 tion of some or all of these causes. 



From what has already been said it will be clear that the 

 first hypothesis is quite inadequate to solve our difficulties. In 

 other branches of botany the reconciliation of opposing state- 

 ments has frequently been attained to by a more careful 

 attention to synonymy; but it should be pointed out that 

 Agardh and Harvey are practically our sole authorities for 

 Australia and New Zealand, so that there is here likely to be 

 but little confusion owing to varying estimates of specific and 

 generic differences. In the other districts referred to the 

 naming of the species has been carried out with the greatest 

 care by recent investigators. Contrasts may be lessened in 

 some cases by further investigation, but resemblances are 

 much more likely to be strengthened than diminished ; and 

 many species are so distinct and so abundant where they do 

 occur that the negative evidence of their omission from a list 

 must be regarded as satisfactory proof that they do not occur 

 in the district. 



The second conjecture need not detain us long. The only 



