- [Footnote: Botanique, p. 106, 120, and 700; Darwin, Journal of
Researches, 1845, p. 433). Morphological laws in the development of the leafy organs determine the peculiar character of the effects produced, the outlines of light and shade. "Phyllodias," says Kunth, "can, according to my view, only occur in families which have compound pinnated leaves; and in point of fact they have as yet only been found in Leguminosæ, (in Acacias). In Eucalyptus, Metrosideros, and Melaleuca, the leaves are simple (simplicia), and their edgewise position arises from a half turn or twist of the leaf-stalk (petiolus); it should be remarked at the same time that the two surfaces of the leaves are similar." In the comparatively shadeless forests of New Holland the optical effects here alluded to are the more frequent, as two groups of Myrtaceæ and Leguminosæ, species of Eucalyptus and of Acacia, constitute almost the half of all the greyish green trees of which those forests consist. In addition to this, in Melaleuca there are formed between the layers of the inner bark easily detached portions of epidermis which press outwards, and by their whiteness remind the European of our birch bark.
The distribution of Myrtaceæ is very different in the two continents. In the New Continent, and especially in its western portion, it scarcely extends beyond the 26th parallel of north latitude, according to Joseph Hooker (Flora antarctica, p. 12); while in the Southern Hemisphere, according to Claude Gay, there are in Chili 10 species of Myrtus and 22 species of Eugenia, which, intermixed with Proteaceæ (Embothrium and Lomatia), and with Fagus]*
