262 Tr ansae tions. — Botany. 



Originally such dune forests" must have been very dense; 

 even now the trees are quite close in many places. On the 

 dunes facing Petre Bay in more than one locality the liane 

 Muhlenbcckia adpressa may be seen climbing over the Olearias, 

 with its numerous interlacing, bare, rope-like stems. 



Compared with the sand-dunes of most parts of New Zea- 

 land! a marked difference lies in the extreme closeness with 

 which the arborescent vegetation of the Chatham Island dunes- 

 approaches the shore. This has been brought about, I should 

 imagine, by the general moisture of the atmosphere, the 

 extremely equable climate, and the freedom from periods of 

 drought. In such a climate as this, as long as the dunes are 

 stable, there is little hindrance to trees, especially those of 

 xerophytic habit, establishing themselves and driving the 

 original sand-fixing vegetation towards -the sea into an ever- 

 decreasing area, until finally such plants, with their special 

 adaptations against drought and salt m the soil on the one 

 hand and instability of the substratum on the other, would 

 be confined to the narrow zone where in the least changed 

 portions of the sand-dune formation they are now to be 

 found. Moreover, the sand usually, or perhaps alwavs, over- 

 lies a layer of peat, and this will be of great benefit for tree- 

 growth. As an example of how a sand-dune forest might 

 originate, my notes furnish the following clue: "On the 

 sand-dunes between Waitangi and Te One Pimelea arenaria 

 occurs in large quantities, forming fixed dunes. Where this 

 plant has quite conquered the drifting sand" — this is, of 

 course, recent drifting sand caused by the destruction of the 

 original vegetation by cattle and sheep — "it encourages 

 the growth of other plants — e.g., Accena, Ghiaphalium luteo- 

 album, and even young seedling plants of Olearia traversii." 

 With no enemy to trample it down or feed upon it, and under 

 the shade of the Pimelea, 0. traversii, thanks to its ran id 

 growth, would soon be well established, and with its enor- 

 mous number of "seeds" and their extreme suitability for 

 wind dissemination, to say nothing of its xerophytic structure, 

 young plants would soon be established in all favourable 

 localities. Olearia traversii, as it occurs on the dunes, is a 

 low tree, with a rather dense head of foliage and a bare trunk 

 covered with rough bark. The leaves are 5 5 cm. long by 

 2-5 cm. broad, or shorter and narrower. They are rather 

 thick but soft, of a bright shining-green on the upper surface 

 and with the under-surface clothed with extremely dense 



* The more inland part of the dune forests are treated of under the 

 heading " Lowland Forest." 



f For an account of certain sand-dunes in the North Island of 

 New Zealand, see Cheeseman (Trans. N.Z. Inst., vol. xxix., p, 364). 



