chap, xxm.] 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 embank- 
ments, 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 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. Aus- 
tralis. 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. 
v “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. 
I I 
