
LIMITS TO THE RANGE OF PLANT-SPECIES. “PVS 
limiting factors for fresh-water forms are, first of all, the existence 
of lochs or running water, and then the depths, character of the 
bottom, isothermal lines, and altitudes. 
If we subtract all these groups from the British Flora, we have 
left the natural wild plants of the woods, Bramble clumps, Broom 
and Whin lands, river-sides, and so on, If we consider the changes 
the country has passed through, even in the historic period, the 
destruction of the Caledonian Forest, replanting, the introduction 
of Larch woods, the abandoning of Larch for other trees, the 
planting of sand-dunes and peat-mosses, and so on, it is obvious 
that it is, in the highest degree, rash to say that any species 
whatsoever is growing in its natural position. Still, there have 
probably always been uncultivated wooded spots in the country to 
which the Melica, Asperula, and Anemone could fly when any 
particular wood was cut down, and from which they could settle 
a new plantation. 
Who could trace a species through these changes of place, even 
in one country? It is obvious that it must be the proper habitat 
and climate which limit their range, and nothing else. 
Tt follows, I think, that we may in some cases distinguish 
indispensable conditions for the ranges of certain species. These 
are as follows:— 
For halophytes—the existence of salt in the soil. 
For chalk and limestone plants—geological boundaries, 1.¢., 
the presence of lime in the soil. 
For peat plants—the presence of peat. 
For Alpine plants—mountains of sufficient altitude, with a 
series of appropriate habitats. 
For weeds of agriculture—agriculture carried on in a manner 
which varies with each individual weed. 
For forage plants and those consciously introduced by man— 
a certain intelligence in agriculture, varying in a similar 
manner. 
For water plants—the presence of running or stagnant 
water, with the required depth and bottom, and also 
with appropriate temperature. 
For road-side, waste, shale, ballast, and railway plants—a 
certain level of human civilisation, and also geological 
boundaries. 
