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Show 480 ISLAND LIFE. (P.A.UT II. . These islands are more thn.n identical with European species. ~ · Cb t . • i and as we have already seen m . ap ei 800 miles from Europe, ' . 0' that they hrwe ever been XII th e is no reason for supposmo . ., er with it than they are now, smce an exten-more nearly connected h 1 OOO-fathom line would very · f th European coast to t e ' . s1on o e . N 't · s a most interestmg and 1. 1 d the dtstance ow I 1 Itt e re. uce - .th half the European genera which suo·o-est1ve fact that more an A 1 · oo 1• fl cur also in the zores, anc 111 occur in the Austra ran ora oc . . 1 Th . several cases even t ,n e speC.i es are identical m both. e 1m-h , this cannot be exaggerated, because Portance of sue a case as I . it affords a d emons t rat w. n of the power of the very p ants lil uesti.O n to pass over WI' d e a reus of sea ' some no doubt whoJly qth rouO'h the ai·r , carn·e d by storms in the same way as tho Europb ean b1' r d s and m· sects· which annually r. eac.h the Azores, others by fl oa tm. g on the waters ' or by a c.o mbmat10n o· f t·h e tw.o methoc l s ; wh 1'l e sorr,e mac. y have been earned by aq• uati• c b1rds, to wh ose 1~ eat h ers many seecls· have the power of attachm. g thcm- selves. W e h ave 1·1 1 such facts as these a complete d1sp•r oof of the necessi' ty 1~ 0r tl1 0s e great chanoo· es of s. ea and land wht.c h arc cont·m ua1 1 Y appea1 e d to by those ·who thmk l·a nd-c· onnefc tiOn· tbe only e ffi e1· en t means of accountinob- for the m1grn.t10n o · annnals or plants ; b u t a t the same time we do not ne.g lect . to make th e fullest use of sueh moderca. te chanoo· es as all the evidence at our comman d 1e ad s us to believe have a. ctually .o ccu.r red,d and espec1·a 11 y of the former existence of mtermedmte Islan s, so of ten I· nd I' Ca t e d by shoals in the midst of the deepest oceans. L Means by which Plants have mig·1~ated frorn NoTth to Sout'.~·- But if plants can thus pass in considerable numbers and van ety over wide seas and oceans, it must be yet more easy for. them. to traverse con t1·n uous areas of ]and ' wherever mo. untam-.c ha. ms I:[! 'table stations at moderate intervals on winch they m1ght ouer SUI .1. · ff d d f · temporarily establish themselves. Th~ fac1 Ities a or e . Ol the transmi·s si·o n of plants by mountams h.a s hardly recmvod sufficient attention. The numerous land-sh~s, the fresh sur-faces of broken rock and precipice, the debT~s of torrents, ~nd the moraines deposited by glaciers, afford numerous unoccupwd 1 IIooker, On the Flom of Au.stmlia., p. 95.-II. C. Watson, in Godlllan's Azores, pp. 278-286. CHAP. XXIll.] ARCTIC PLANTS IN NEW ZEALAND. 481 stations on which wind-borne seeds have a good chance of germinating. It is a well-known fact that fresh surfaces of soil or rock, such as are presented by railway cuttings and embankments, often produce plants strange to the locality, which survive for a few years, and then disappear as the normal vegetation gains strength and permanence.1 But such a surface will, in the 1 As this is a poi'nt 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, Jfelilotus vulga1·is made its appearance on the banks, remained for several years, and then altogether disappeared. Another case is that of Diplotaxis mttraUs, 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 v1rgm 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. A ustmlis. 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 arouud 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. II. C. Watson has been kilH~ enough to send me a detailed account of the progress of vegetation on the rnilway banks and cuttings about rrhames Ditton. This account is written from memory, but as Mr. Watson states that he took a great interest in watching the procef:lf:l 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, lsatis 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. I I |