AN a^COLOOICAL PItOBLEM. 233 



found on the quartzite schists in this country, but is a common 

 plant in Scandinavia, and seen by myself on many different rock 

 formations. Thus we find that so far as our extremely rare 

 plants are concerned they are not confined to any one rock 

 formation, and if we examine the list of what I have termed the 

 very rare arctic or alpine plants, thirty-two of which occur in this 

 country, we discover that only thirteen of them occur on Ben 

 Lawers ; in short, the wider we make the range the more varied 

 do the soils on which the plants grow become. 



In view of these facts I think there is some reason for 

 doubting that any one rock formation has much influence in 

 determining what plants will grow on it. That plants appear to 

 grow better on some rock formations than on others, is not to be 

 denied. But that chemicals set free by the decomposing rock is 

 the sole cause of this is very questionable. The pockets formed 

 by some of these laminated and contorted schists provide a good 

 foothold for plants, and that this is an important factor cannot 

 be gainsaid, and also that the disintegrating rock which fills these 

 pockets forms a suitable nidus for the plants is undeniable — the 

 mica on the roots of all our alpine plants in Herbaria proves this ; 

 but again if this disintegrated rock were better adapted than 

 other rocks for the propagation of alpine plants it shoukl be 

 shown on the detritus. Let us consider the detritus of Ben 

 Lawers where it is composed of phylite schist ; that of Creag-na- 

 Caillich where it is quite apparent that a fair proportion of lime 

 is mixed with the soil ; that of Ben More where we have pure 

 black schist, and that of Beinn Laoigh where we have black and 

 phylite schists. In all these cases the detritus is at an elevation 

 of from 2,000 to 3,000 feet, and we find only five plants, namely : 

 — Cerastiuni alpinu7n, Sagina Liimcei, Silene acanlis, Alchemilla 

 alpina, Sibhaldia procumbens. common to the four mountains. 

 At first sight this looks as if the rock composition might be 

 influencing distribution, but on looking a little closer into the 

 matter, we see that all the plants found on the detritus of any of 

 these mountains will be found on different parts of the different 

 mountains with four exceptions, namely, Sagina nivalis, Arenaria 

 sulcata, and Myosotis alpestris confined to Ben Lawers, and Arabis 

 petraea confined to Beinn Laoigh. Now, it is quite evident that 

 the xerophilous nature of some soils has a very great influence on 



