OVER THE HILLS AND FAR AWAY 25 



result. In lichens it is the Fungus that forms the fruit- 

 ing body, but the Alga enters into the partnership 

 almost from the very first. In wet weather the surface 

 of the lichen is often covered with a mealy powder that 

 appears from within. The powder consists of minute 

 contributions from both partners and it represents a 

 vegetative way of multiplying, for it gets carried about 

 by the wind. 



As we look about we see several different kinds of 

 lichens, and it is interesting to make a collection in a 

 box. Some are flat encrustations, some are leaf-like, 

 some are hairy, and so on; many are finely coloured. 

 It seems a far cry from the top of a mountain to the 

 chemical laboratory, but the litmus-paper that is so 

 much used because it changes colour on the presence 

 of any acid is made from lichens. The Reindeer Moss 

 (Cladonia rangiferina), on which reindeer largely 

 depend, and the Iceland Moss (Cetraria islandica), 

 which is used for making a delicate invalid's food, are 

 both lichens and not uncommon on British mountains. 

 How many interests intersect even in the lichens of 

 this hilltop ! 



We must not stay, but there are two interesting 

 points which we cannot miss that lichens begin in 

 many cases the process of soil-making, and that, 

 though they are very resistant to extremes of cold and 

 heat, they are very sensitive to impurities in the air. 

 They are creatures of the clean open air. Along with 

 the lichens on the mountain-top there are some hardy 

 mosses, notably the woolly Fringe Moss (Rhacomi- 

 trium lanuginosum\ which sometimes spread like a 

 carpet and form the beginning of moss peat at high 

 altitudes. 



