Cockayne. — On Vegetation of Open Bay Islands. 369 



Islands. From their structure, and from what is known re- 

 garding the geological history of New Zealand, they evidently 

 at no very distant date formed a portion of the mainland. 

 It seems, then, instructive from a phytogeographical point of 

 view to give a brief sketch of their vegetation, at the same time 

 comparing it with that of the adjacent coast, so that the effect 

 of isolating such coastal vegetation upon a gradually diminishing 

 land-area and exposing it in consequence to slowly increasing 

 unfavourable conditions may be estimated. The importance 

 of this study is also very much enhanced from the fact that 

 the vegetation of the islands is quite in its primeval condition, 

 there having been no settlement of any kind, and, so far as I 

 could observe, with the exception of a few plants of Poa annua, 

 introduced plants are absent. 



Now, the coast of Westland, thanks to the excessive rain- 

 fall of more than 254 cm. yearly, is covered almost to high- 

 water mark with a dense forest, made up of numerous species 

 of plants, but which differ in numbers and grouping according 

 to the drainage conditions of the ground. Such a forest is, 

 however, a typical evergreen rain-forest, and contains many 

 epiphytes, lianes, tree-ferns, mosses, and liverworts. As for 

 the lianes, the tree-trunks are frequently so thickly covered 

 with climbing species of Metrosideros or Freycinetia banksii 

 that their bark is quite hidden. With forest similar to the 

 above would the Open Bay Islands be covered when forming 

 part of the mainland. 



During a trip in the Government steamer " Hinemoa " I 

 had the rare opportunity of visiting these islands, in February, 

 1903, and it is from notes hastily taken during that visit that 

 this paper is compiled. 



The islands are two in number, divided from each other 

 by a narrow strait. The larger and more northerly of the two 

 is perhaps at most half a mile in length. On the east its surface 

 terminates abruptly in precipitous cliffs, ranging in height from 

 15 m. to 30 m., but towards the west it gradually slopes to the 

 sea. To the north and west are many flat rocks, which are 

 left quite bare at low water. At the southern extremity this 

 island is cut into two unequal parts by a deep chasm, through 

 which the sea dashes at high water. The smaller island con- 

 sists of a low conical hill 45 m. or thereabouts in height. 



Both islands are formed of limestone, which is overlaid by 

 a rather deep covering of soil, consisting of coarse, dark-coloured 

 peat, containing a considerable percentage of imperfectly de- 

 cayed vegetable matter. This soil is extremely loose, both from 

 its texture and from being honeycombed with the holes of 

 mutton-birds. It is also saturated with water, so that, when 



24— TranF. 



