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Show 482 ISLAND LIFE. [PART IT. meantime have acted as a fresh centre of dispersal ; and thus a plant might pass on step ·by step, by means of stations temporarily occupied, till it reached a district where, the "Close by Ditton Station three species appeared which m~y be called m· ter1 o pera. Tl1 e biennial Barbarea p1·ecox ' one· of these, h1 sf .t he least . ·I bl b use I't rnight have come as seed m the eart I Om some 1 emar m e, .ec9. b 11 ) A fi · gard en~ or possi' bly in the Thames gravel (used as a astd . ·n t rst .1 t increased to several plants, then became less numerous, an ~1 s?on, .m all probability, become extinct, crowded out by ?ther plants. The bienmal Petroselinum seget'urn was at first one very luxunant plant on the sl?pe of the embankment. It increased by seed into a dozen 01: a s~ore, and IS now nearly if not quite extinct. The third species is Lmarta purpurea, not strictly a British plant, but one established in some places on old walls. A sino le root of it appeared on the chalk facing of the embar)km~nt by Ditto~ Station. It has remained there several years and grown mto. a vi·g orous speet·m en · Two or three smaller examples are nowf seedn by 1t, doubtless sprung from some of the hund_reds or _thousand~ o see s shed by the original one plant. The species IS not mcluded m Salmon an~l Brewer's Flora of Sun·ey. . . . "The main line of the railway has introduced mto D1tton pansh the perennial A mois hi1•8uta, likely to become a pern:unent inhfabitan1t~1 Tho Hpecies is found on the chalk .and gre~msand nn~es away .·rom utmes Ditton ; but neither in this pansh nor m any adJacent p::msh, so far ~s }:nown to myself or to the authors of the flora of t~e county, does ~t occur. Some years after the railway was made a SI~gle root. of th~s Arabis was observed in the brickwork of an arch by whwh the rmlway JS carried over a public road. A year or two afterwards th?re were three or four plants. In some later year I laid some of the npened 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 tl~e arch. It is presumable that the first seed may ~ave been brought f~om Gml~ford. But how could it get on to the perpendicular face of the bnekwork. "The Bee Orchis (Ophrys apije1·a), plentiful on some of the chalk lands in Surrey, is not a species of Thames Ditto?, or (as I presume) of any adjacent parish. Thus, I was greatly surpnsed some years _back to see about a hundred examples of it in flower in one clay?y field either_o? ~he outskirts of Thames Ditton or just within the limits of the adJ~mmg parish of Cobham. I had crossed this same field in a former year without observing the Ophrys there. And on finding i~ in the on~ fi~ld I closely searched the surrounding :fields and copses, without fin.dmg It anywhere else. Gradually the plants became fewer and fewer m that on~ field, and some six or eight years after its first discover~ there the sp?Cies had quite disappeared again. I guessed it had been mtroduced w1th 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 cuttmgs on the CUAP. XXIII.] AUCTIC PLANTS IN NEW ZEALAND. 483 general conditions being more favourable it was able to establish itself as a permanent member of the flora. Such ~encr~lly :"peaking, was probably the process by which th~ Scandmav1an flora has made its way to the southern hemisphere; but it could hardly have done so to any important r~ilway from Yarmouth to Caistor in N.orfolk, where it passes over extenSl~ e Aandy Denes with a sparse vegetat,ion. The first year nfter tl1e rmlway was made the banks produced abundance of CEnothet·a od01·ata t~nd JJ_elphinit~n~ Ajatis (the latter only known thirty miles off in cornilelds ~~ Cambndgeshire), with At1'iplex patula and A. deltoidea. Gradually the nattve sand plants- Carices, Grasses, Galium venun, &c., established t~1emselves, and year by year covered more ground till the new introduc~ JOn~ alm~st co~pletely disappeared. The sarue phenomenon was observed m. Can:bndgeslnre between Chesterton aliCl Newmarket, where, tho soil bemg different, Stellaria media and other annuals appeared in large patches ; but these soon gave way to a permanent vegetution of grasses, composites, &c., so that in the third year no Stella1·ia 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 Mille Thistle ( Ca1·duus ma?"ianus) have been known for the past fifteen years; ?ut although they seeded freely, the seeds had no opportunity of gcnninatmg, so that the thistle did not spread. A remarkable exception to this rule occurred during the formation of the Onehunga railway, where a few se~ds fell on di:stur~ed soil, grew up and flowered. The railway works bemg suspended, the plant increased rapidly, aud spread wherever it could find disturbed soil." Again:-" The fiddle-dock (Rumex pulchm·) occurs in great abundance on the formation of new streets, &c., hut soon becomes comparatively rare. It seems probable ilwt it was one of the earliest plants naturalised here but that it partially <.li0J 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. t The preceding examples of the temporm·y establishment of plnnts 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 l1as received little attention, and is not even referred to in the elaborate work of De Candolle ( Geographie Botanique Raisonnee) 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. 1 Tmnsactions of the New Zealand Institute, Vol. X. p. 367. I I 2 |