as detailed for tropical rain forest, Richards (1952). A rectangular strip of forest 25ft wide by (preferably) 200ft in length is marked out, and all trees are drawn to scale on a graphed board while facing one side of the strip. Undergrowth species up to 10ft are ignored, and the results are recorded as a profile diagram showing a profile transect of the forest structure to scale. Each profile diagram is accompanied by full ecological notes. In the Orongorongo valley the podocarp-broadleaf forest type is illustrated by Fig. 4. Structurally three tree strata may be recognised:- 1. An upper stratum of podocarp species showing a tendency towards grouping. The height is between 80–100 feet and the layer is almost continuous with the rimu (Dacrydium cupressinum) the most prevalent species. Fig. 3.—Detail of the lower part of Green's Stream, near junction with Orongorongo River, showing avalanche terraces, A, B, C. 2. A middle stratum forming a discontinuous layer between 40–80 feet and composed of broadleaf trees—Knightia excelsa, Elaeocarpus dentatus, Weinmannia racemosa. 3. A lower stratum forming a continuous stratum between 10–30 feet in height and composed of small trees and tall shrubs with greater variance in heights than those of the higher strata. The predominant species are Melicytus ramiflorus and Hedycarya arborea. In places there is a dense supporting growth of Pseudowintera axillaris, as shown in Fig. 4. Epiphytes, lianes and tree ferns are conspicuous features. Below these three tree strata, recorded only on the ecological data sheets, is a layer of small woody shrubs and tree ferns and young seedling trees of the upper strata sparse in density and averaging between 3–4 feet in height. The field layer is composed of seedlings, ferns and graminoid herbs with mosses covering trunk bases, exposed roots and fallen logs. However, there is little doubt that the lowland podocarp-broadleaf forests of the Orongorongo valley are in the process of a slow change towards northern rata (Metrosideros robusta) dominated forests. The rata is initially an epiphytic plant in the crown of the podocarps (most commonly the emergent Dacrydium cupressinum) and sends down long adventitious roots which entwine the host tree and finally reach the floor of the forest. In time the crown of the host tree is shaded out by the spreading growth of the more vigorous Metrosideros which eventually replaces the host completely. By this time the aerial roots of the Metrosideros have increased enormously in girth and encircle the trunk of the host and become self supporting.