220 OLAF GALLOE 
Pendulous fruticose lichens can be found on rocks of all . 
degrees of inclination: horizontal surfaces, vertical and sloping rock- 
faces, etc. 
The associations may be — as in the case of the phanerogams 
— divided into formations, facies or whatever we may choose to 
call them, and they may be named after the one or more species 
which dominate the community. 
In addition to the chemical and physical qualities of the rock 
and the degree of inclination of the substratum, there are other 
conditions which play a part as regards the physiognomy of the 
vegetation, primarily conditions pertaining to moisture, and the 
competitive relations between the species themselves. 
Thus the same vegetations are not found on rocks wetted with 
spray, on submerged rocks and on dry emergent rocks. The quality 
of the water also — salt, fresh or distilled (rain) water — plays an 
essential rôle here. Moreover, it is of no slight importance, whether 
the rocks are frequently manured by birds or whether this does 
not take place. 
We can, as already mentioned, divide the associations, which 
are produced by the action of each of these complexes of life-con- 
ditions, in very different ways: we may speak of “nitrophilous 
associations” (Sernander), of halophilous associations, associations 
of hollows, associations of horizontal surfaces, etc., according to our 
knowledge of the factors which determine the association. But this 
mode of naming them appears to me to be extremely unpractical, 
because we may very often be at a loss with regard to the group 
to which we are to refer the association in question. It is in reality 
not at all possible to draw a decided line between a nitrophilous 
and a non-nitrophilous association: all lichens are in fact nitro- 
philous to some degree. 
It is the same difficulty with which the ecologists have had to 
contend as regards the soil-associations, but in this department order 
is appearing owing to the fact that the association is not named 
after factors — as a rule imperfectly known — which condition its 
well-being (‘“sand-vegetation,” ‘‘rock-vegetation,’ ‘“xerophilous cop- 
pice,’ etc.), but after the plants themselves (phanerophyte-vegetation, 
chameephyte-vegetation, etc.). 
Whether one choose the one or the other mode of procedure 
is by no means a matter of indifference. The associations living in 
nature are naturally the same, whether we give them the one or 
