
LIMITS TO THE RANGE OF PLANT-SPECIEs. 209 
down of a wood, may entirely alter the range of a species. Mr. 
Dow has recorded the disappearance of Goodyera repens, R. Br., 
from Longforgan, and Mr. Smith’ from St. Fort Wood, through 
this very simple cause. Drainage, railway and road-making 
operations, all produce marked, definite, and distinct changes in 
the flora. In this country the flora is wholly artificial over 
nineteen-twentieths of the surface ; really wild plants are confined 
to odd corners, banks, shingle-beds, &c. 
The best and clearest cases of naturally and definitely limited 
range are found with certain marine plants. All true halophytes, 
such as Suda, Salsola, and Aster Tripoliwm, Linn., have in 
course of time become adapted to salt-congested ground, and the 
presence of salt is a sine qud non, in nature, of their existence. 
If the salt be by any means removed, they are choked out by 
others, just as the Mangrove is only able to flourish whilst the 
sea water comes to its roots. When the soil rises above the level 
of the tide, the Mangroves are choked out by the West Coast 
Jungle.* Yet, even in this respect, one must not be too certain, 
Najas marina,* Linn., was a fresh-water plant in the inter-glacial 
period, it now lives in brackish or salt water; and other plants 
may be altering their habits. 
There are two other cases in which soil is admitted by most 
people to distinctly limit specific range, viz., in plants confined 
to peat or limestone countries. Of the two, peat, in my own 
experience, exercises the more rigorous selection. Yet almost 
all plants which are found on peat would grow in other places, 
if they were allowed to do so by the struggle for existence. Such 
a species as Potentilla Tormentilla, Scop., is extremely common, 
even dominant, on peat, but it also grows perfectly well on other 
soils. Limestone and chalk plants are not so distinctly limited, 
for it is only on bare exposed knolls and rocks that the character- 
istic lime-loving species are found, or, at any rate, only where the 
limestone can really affect the plant, There are, however, a few 
plants to whose distribution peat or limestone is of the nature 
of a sine qud non. 
1 Smith, Proc. Perthshire Soe. Nat. Science, Vol. II., Part vi., 1898. 
? Colonial Reports, Miscellaneous, No. 3, p. 6. 
° Krause, Botan. Centralblatt, Bd. LXXV., No. 3, p. 66. 
