Oliver. — Vegetation and Flora of Lord Howe Island. 109 



Autecology of Coastal-scrub Plants.— An aqueous hypoderm is present in 

 Coprosma prisca, Ochrosia elliptica, and Lagunaria Patersoni, but not in 

 Celtis amblypkylla, where the palisade tissue occupies half the mesophyll. 



Hill Scrub. 



On the top of sea-cliffs and on exposed ridges and cliffs on the moun- 

 tains forest gives way to scrub identical in structure with coastal scrub, 

 but containing quite another association of species. 



On the Northern Hills the scrub on the ridges is 1 m. to 2 m. high, 

 and composed of dense, close-growing shrubs. It usually forms an im- 

 penetrable mass of vegetation, with no undergrowth ; but where the foliage 

 is more lax or broken an undergrowth of low ferns and grasses appears. 

 The following species of shrubs are usually present : Cassinia tenuifolia, 

 Baloghia lucida, Dodonaea viscosa, Rapanea platy stigma, Pimelea congesta, 

 Notelaea quadristaminea, Myoporum insulare, Lagunaria Patersoni, Hemi- 

 cyclia australasica, Cryptocarya Gregsoni, Jasminum simplici folium, and 

 Alyxia ruscifolia. 



The undergrowth, where present, may contain Adiantum aethiopicum, 

 Poa caespitosa, Asplenium nidus, and on light rocky places Platycerium 

 bifurcation. 



Scrub similar in structure and floristic composition to that just described 

 is found in exposed places at low elevations on the mountains. 



4. Low Succulent Plants. 

 Lobelia-Mesembryanthemum Association . 



In the gap between Mount Eliza and North Head the wind continually 

 sweeps through, usually with great violence. Here there are no trees and 

 only a few detached shrubs, but the area is occupied by formations of 

 herbaceous plants. In the most exposed portion are low succulent plants, 

 while leeward of these is a rush formation. On windy days the whole 

 valley is drenched with salt spray. On the slope facing the sea there are 

 a few detached rounded shrubs of Melaleuca ericifolia. Except for these 

 the ground is entirely covered with a low even growth of succulent herbs 

 15 cm. to 20 cm. high. Mesembryanthemum aequilaterale and Lobelia anceps, 

 together with some Cynodon dactylon, are fairly well mixed. On the 

 crest of the ridge small plants of Scirpus nodosus occur, while Melaleuca 

 ericifolia disappears. 



Salicornia Association. 



On coastal rocks just above high-water mark there occurs in West Bay 

 several small patches of Salicornia australis. 



5. Sand-binders. 



Ned's Beach. — -Below the scrub is a formation of herbaceous plants 

 covering the steep slope of a headland. The soil is chiefly loose limestone 

 rock undermined by shearwaters (Puffinus carneipes), which burrow out 

 heaps of looose sand. The soil is therefore very dry and not unlike a sand- 

 dune. The dominant plants are a trailing sand-binding grass, Spinifex 

 hirsutus, and a trailing herb, Wedelia uniflora, fairly evenly intermixed. 

 With these are associated several herbaceous plants, all, however, of 

 secondary importance. Fairly common are Lepidium howei - insidae 



