Island Life; Or, The Phenomena and Causes of Insular Faunas and Floras

15. Tetranthera. Tropical Australia, Tropics.

16. Santalum. Tropical and Sub-tropical Australia, Pacific, Malay Islands.

17. Carumbium. Tropical and Sub-tropical Australia, Pacific Islands.

18. Elatostemma. Sub-tropical Australia, Asia, Pacific Islands.

19. Peperomia. Tropical and Sub-tropical Australia, Tropics.

20. Piper. Tropical and Sub-tropical Australia, Tropics.

21. Dacrydium. Tasmania, Malay, and Pacific Islands.

22. Dammara. Tropical Australia, Malay, and Pacific Islands.

23. Dendrobium. Tropical Australia, Eastern Tropics.

24. Bolbophyllum. Tropical and Sub-tropical Australia, Tropics.

25. Sarcochilus. Tropical and Sub-tropical Australia, Fiji, and Malay Islands.

26. Freycinetia. Tropical Australia, Tropical Asia.

27. Cordyline. Tropical Australia, Pacific Islands.

28. Dianella. Australia, India, Madagascar, Pacific Islands.

29. Cyperus. Australia, Tropical regions mainly.

30. Fimbristylis. Tropical Australia, Tropical regions.

31. Paspalum. Tropical and Sub-tropical grasses.

32. Isachne. Tropical and Sub-tropical grasses.

33. Sporobolus. Tropical and Sub-tropical grasses.

188

Insects are tolerably abundant in the open mountain regions, but very scarce in the forests. Mr. Meyrick says that these are "strangely deficient in insects, the same species occurring throughout the islands;" and Mr. Pascoe remarked that "the forests of New Zealand were the most barren country, entomologically, he had ever visited." (Proc. Ent. Soc., 1883. p. xxix.)

189

Introductory Essay On the Flora of Australia, p. 130.

190

Hooker, On the Flora of Australia, p. 95.—H. C. Watson, in Godman's Azores, pp. 278-286.

191

As this is a point of great interest in its bearing on the dispersal of plants by means of mountain ranges, I have endeavoured to obtain a few illustrative facts:—

1. Mr. William Mitten, of Hurstpierpoint, Sussex, informs me that when the London and Brighton railway was in progress in his neighbourhood, Melilotus vulgaris made its appearance on the banks, remained for several years, and then altogether disappeared. Another case is that of Diplotaxis muralis, which formerly occurred only near the sea-coast of Sussex, and at Lewes; but since the railway was made has spread along it, and still maintains itself abundantly on the railway banks though rarely found anywhere else.

2. A correspondent in Tasmania informs me that whenever the virgin forest is cleared in that island there invariably comes up a thick crop of a plant locally known as fire-weed—a species of Senecio, probably S. Australis. It never grows except where the fire has gone over the ground, and is unknown except in such places. My correspondent adds:—"This autumn I went back about thirty-five miles through a dense forest, along a track marked by some prospectors the year before, and in one spot where they had camped, and the fire had burnt the fallen logs, &c., there was a fine crop of 'fire-weed.' All around for many miles was a forest of the largest trees and dense scrub." Here we have a case in which burnt soil and ashes favour the germination of a particular plant, whose seeds are easily carried by the wind, and it is not difficult to see how this peculiarity might favour the dispersal of the species for enormous distances, by enabling it temporarily to grow and produce seeds on burnt spots.

3. In answer to an inquiry on this subject, Mr. H. C. Watson has been kind enough to send me a detailed account of the progress of vegetation on the railway banks and cuttings about Thames Ditton. This account is written from memory, but as Mr. Watson states that he took a great interest in watching the process year by year, there can be no reason to doubt the accuracy of his memory. I give a few extracts which bear especially on the subject we are discussing.

"One rather remarkable biennial plant appeared early (the second year, as I recollect) and renewed itself either two or three years, namely, Isatis tinctoria—a species usually supposed, to be one of our introduced, but pretty well naturalised, plants. The nearest stations then or since known to me for this Isatis are on chalk about Guildford, twenty miles distant. There were two or three plants of it at first, never more than half a dozen. Once since I saw a plant of Isatis on the railway bank near Vauxhall.

"Close by Ditton Station three species appeared which may be called interlopers. The biennial Barbarea precox, one of these, is the least remarkable, because it might have come as seed in the earth from some garden, or possibly in the Thames gravel (used as ballast). At first it increased to several plants, then became less numerous, and will soon, in all probability, become extinct, crowded out by other plants. The biennial Petroselinum segetum was at first one very luxuriant plant on the slope of the embankment. It increased by seed into a dozen or a score, and is now nearly if not quite extinct. The third species is Linaria purpurea, not strictly a British plant, but one established in some places on old walls. A single root of it appeared on the chalk facing of the embankment by Ditton Station. It has remained there several years and grown into a vigorous specimen. Two or three smaller examples are now seen by it, doubtless sprung from some of the hundreds or thousands of seeds shed by the original one plant. The species is not included in Salmon and Brewer's Flora of Surrey.

"The main line of the railway has introduced into Ditton parish the perennial Arabis hirsuta, likely to become a permanent inhabitant. The species is found on the chalk and greensand miles away from Thames Ditton; but neither in this parish nor in any adjacent parish, so far as known to myself or to the authors of the flora of the county, does it occur. Some years after the railway was made a single root of this Arabis was observed in the brickwork of an arch by which the railway is carried over a public road. A year or two afterwards there were three or four plants. In some later year I laid some of the ripened seed-pods between the bricks in places where the mortar had partly crumbled out. Now there are several scores of specimens in the brickwork of the arch. It is presumable that the first seed may have been brought from Guildford. But how could it get on to the perpendicular face of the brickwork?

"The Bee Orchis (Ophrys apifera), plentiful on some of the chalk lands in Surrey, is not a species of Thames Ditton, or (as I presume) of any adjacent parish. Thus, I was greatly surprised some years back to see about a hundred examples of it in flower in one clayey field either on the outskirts of Thames Ditton or just within the limits of the adjoining parish of Cobham. I had crossed this same field in a former year without observing the Ophrys there. And on finding it in the one field I closely searched the surrounding fields and copses, without finding it anywhere else. Gradually the plants became fewer and fewer in that one field, and some six or eight years after its first discovery there the species had quite disappeared again. I guessed it had been introduced with chalk, but could obtain no evidence to show this."

4. Mr. A. Bennett, of Croydon, has kindly furnished me with some information on the temporary vegetation of the banks and cuttings on the railway from Yarmouth to Caistor in Norfolk, where it passes over extensive sandy Denes with a sparse vegetation. The first year after the railway was made the banks produced abundance of Œnothera odorata and Delphinium Ajacis (the latter only known thirty miles off in cornfields in Cambridgeshire), with Atriplex patula and A. deltoidea. Gradually the native sand plants—Carices, Grasses, Galium verum, &c., established themselves, and year by year covered more ground till the new introductions almost completely disappeared. The same phenomenon was observed in Cambridgeshire between Chesterton and Newmarket, where, the soil being different, Stellaria media and other annuals appeared in large patches; but these soon gave way to a permanent vegetation of grasses, composites, &c., so that in the third year no Stellaria was to be seen.

5. Mr. T. Kirk (writing in 1878) states that—"in Auckland, where a dense sward of grass is soon formed, single specimens of the European milk Thistle (Carduus marianus) have been known for the past fifteen years; but although they seeded freely, the seeds had no opportunity of germinating, so that the thistle did not spread. A remarkable exception to this rule occurred during the formation of the Onehunga railway, where a few seeds fell on disturbed soil, grew up and flowered. The railway works being suspended, the plant increased rapidly, and spread wherever it could find disturbed soil."

Again:—"The fiddle-dock (Rumex pulcher) occurs in great abundance on the formation of new streets, &c., but soon becomes comparatively rare. It seems probable that it was one of the earliest plants naturalised here, but that it partially died out, its buried seeds retaining their vitality."

Medicago sativa and Apium graveolens, are also noted as escapes from cultivation which maintain themselves for a time but soon die out. (Transactions of the New Zealand Institute, Vol. X. p. 367.)

The preceding examples of the temporary establishment of plants on newly exposed soil, often at considerable distances from the localities they usually inhabit, might, no doubt, by further inquiry be greatly multiplied; but, unfortunately, the phenomenon has received little attention, and is not even referred to in the elaborate work of De Candolle (Géographie Botanique Raisonnée) in which almost every other aspect of the dispersion and distribution of plants is fully discussed. Enough has been advanced, however, to show that it is of constant occurrence, and from the point of view here advocated it becomes of great importance in explaining the almost world-wide distribution of many common plants of the north temperate zone.

192

Sir Joseph Hooker informs me that he considers these identifications worthless, and Mr. Bentham has also written very strongly against the value of similar identifications by Heer and Unger. Giving due weight to the opinions of these eminent botanists we must admit that Australian genera have not yet been demonstrated to have existed in Europe during the Tertiary period; but, on the other hand, the evidence that they did so appears to have some weight, on account of the improbability that the numerous resemblances to Australian plants which have been noticed by different observers should all be illusory; while the well established fact of the former wide distribution of many tropical or now restricted types of plants and animals, so frequently illustrated in the present volume, removes the antecedent improbability which is supposed to attach to such identifications. I am myself the more inclined to accept them, because, according to the views here advocated, such migrations must have taken place at remote as well as at recent epochs; and the preservation of some of these types in Australia while they have become extinct in Europe, is exactly paralleled by numerous facts in the distribution of animals which have been already referred to in Chapter XIX., and elsewhere in this volume, and also repeatedly in my larger work.

193

Out of forty-two genera from the Eocene of Sheppey enumerated by Dr. Ettingshausen in the Geological Magazine for January 1880, only two or three appear to be extinct, while there is a most extraordinary intermixture of tropical and temperate forms—Musa, Nipa, and Victoria, with Corylus, Prunus, Acer, &c. The rich Miocene flora of Switzerland, described by Professor Heer, presents a still larger proportion of living genera.

194

The recent discovery by Lieutenant Jensen of a rich flora on rocky peaks rising out of the continental ice of Greenland, as well as the abundant vegetation of the highest northern latitudes, renders it possible that even now the Antarctic continent may not be wholly destitute of vegetation, although its climate and physical condition are far less favourable than those of the Arctic lands. (See Nature, Vol. XXI. p. 345.)

195

Dr. Hector notes the occurrence of the genus Dammara in Triassic deposits, while in the Jurassic period New Zealand possessed the genera Palæozamia, Oleandrium, Alethopteris, Camptopteris, Cycadites, Echinostrobus, &c., all Indian forms of the same age. Neocomian beds contain a true dicotyledonous leaf with Dammara and Araucaria. The Cretaceous deposits have produced a rich flora of dicotyledonous plants, many of which are of the same genera as the existing flora; while the Miocene and other Tertiary deposits produce plants almost identical with those now inhabiting the country, together with many North Temperate genera which have since become extinct. (See p. 499, footnote (#x28_x_28_i99), and Trans. New Zealand Inst., Vol. XI. 1879, p. 536.)

196

The fact stated in the last edition of the Origin of Species (p. 340) on the authority of Sir Joseph Hooker, that Australian plants are rapidly sowing themselves and becoming naturalised on the Neilgherrie mountains in the southern part of the Indian Peninsula, though an exception to the rule of the inability of Australian plants to become naturalised in the Northern Hemisphere, is yet quite in harmony with the hypothesis here advocated. For not only is the climate of the Neilgherries more favourable to Australian plants than any part of the North Temperate zone, but the entire Indian Peninsula has existed for unknown ages as an island and thus possesses the "insular" characteristic of a comparatively poor and less developed flora and fauna as compared with the truly "continental" Malayan and Himalayan regions. Australian plants are thus enabled to compete with those of the Indian Peninsula highlands with a fair chance of success.