338 THE DISPLACEMENT OF SPECIES IN NEW ZEALAND. of 'S'. punctulatum Breb., and we therefore call it 8. }mnctulatum Breb. var. coronatum (Schmidle) nob. It is a common thing for the angles of the two semicells in both 8. piwctidatiim and 8. pyg- mcBum to alternate with each other, and not uncommonly the angles of the two semicells in 8. alternans are opposite. The figures of 8. alternajis and 8. dilatatum in Ealfs' British Desmidiem are amongst the most beautiful and most accurate in the whole book, and are exactly like thousands of specimens we have seen from all over the British Isles. S. bicorne Hauptfl. ? Borge {Bihang till K. Sv. vet.-akad. handl. Band 21, afd. iii. p. 24, fig. ^15). This is 8. Pseudosehaldi Wille, "^'Duacense West [Jouni. Linn. 8oc. (Bot.) xxix. p. 184, t. xxiv. fig. 1 (1892). S. protractum Eacib. {Flora, Ixxxi. p. 34, taf. iii. u. iv. fig. 14 (1895) ). This seems to us very like a large form of 8. Icevispinum Bissett. THE DISPLACEMENT OF SPECIES IN NEW ZEALAND. By T. Kirk, F.L.S. '^ In the absence of civilization, the indigenous fauna or flora of any country is liable to little or no change from external causes. Aerial and marine currents may occasionally bring spores or even seeds of exotic plants ; more rarely, insects or birds may be intro- duced by gales of unusual violence ; migratory or aquatic birds may introduce the eggs of insects, or even molluscs, as well as seeds and fragments of terrestrial or lacustrine plants which have become attached to their feathers ; and certain terrestrial or fluviatile molluscs may be introduced by drifted logs ; but after a certain time any increase in the number of species by agencies of this kind must become extremely rare, and can occur only at distant intervals. It nqay therefore be concluded that in all probability the constituents of the fauna and flora of this colony, with possibly the exception of the larger Eatite birds, were in much the same condition when they were first seen by Cook and Vancouver as they had been for many previous centuries. But with the advent of civilization vast and far-reaching changes speedily take place : axe and fire rapidly alter the face of the country ; portions of the forest are felled, burnt off, and replaced by grass — a change which of itself involves a multitude of other changes ; the unfelled portions of the forest are laid open to violent winds, so that the surface-rooting trees are blown over in large numbers, while the increasing dryness of the atmosphere acts unfavourably on the undergrowth, which is still further injured by the depredations of cattle ; gradually the plants less able to resist changed conditions disappear, and with them many insects, lizards,
- Extracted from his Presidential Address to the WeUington Philosophical
Society, 3rd July, 1895.
