8 TRAP-FLORA OF RENFREWSHIRE. 
Then would follow the “ primzval peat” plastered over the 
higher summits. 
The point, however, is that the characteristic rock-face flora 
will not occur. 
Certainly these Renfrewshire rock faces have a characteristic 
association. As members of the Society are aware, there is, as 
yet, no recognised law as to associations and formations. 
Practically every botanist follows his own views. 
Eugen Warming divides the vegetation into some thirty- 
three distinct associations according to the moisture conditions. 
Thus we find a reference to the Ulex association under the 
heading of xerophyten shrubs. Under the rock vegetations there 
is a note of the lichen heaths of the far north, and moss-moors 
come under water vegetation. Woods under mesophytenvereine. 
But as I have shown, the same plot of ground may be 
successively inhabited by five or six of Warming’s associations. 
A. F. W. Schimper starts from quite another point. Taking 
the three great climatic divisions—wood, grass, and desert—which 
depend like those of Warming on the amount of water in the soil 
and atmosphere, he finds in each of these great divisions, 
formations which are governed by the chemical and especially 
physical conditions of the soil, or “ edaphic ” conditions. 
But he says that the formations are not in themselves 
uniform, but show gradations which are due to special climatic 
conditions. 
I think you will at once see how very difficult it is to find the 
place of any special case, such as our Renfrewshire rock flora. 
During the history above described, it is successively covered 
by five or six distinct and different asssociations (Warming’s) 
Viz. :— 
Lichen moor. (Xerophyten or rockjloors.) 
Moss moor. (Polytrichum, Hypnoid), Aygrophyten. 
Vaccinium stage. Alpine meadows. 
Herbaceous stage. Grass meadows. 
Ulex stage. Xerophyten shrubs. 
Rosaceous stage. Jesophyten shrubs. 
Nor is this all. Two of the plants concerned, namely, broom 
and whin, pass during their own life-history from a wet association 
to a dry one. 
OMEN GN 
