THE STORY OF THE LICHENS 107 



makes it possible for lichens to support an 

 existence in such inhospitable places. There is 

 little doubt that these humble plants played a 

 very big part in the early history of this earth, 

 and we must regard them as one of the oldest 

 forms of land vegetation. 



Many people during the summer time have 

 had an opportunity of exploring one of the 

 thousands of rocky inlets around the coastline. 

 The vast number of these are only just above 

 high-water mark, and even the thrift and the 

 coarse sea-grass have been unable to find a 

 foothold. Yet the rocks are golden and 

 green with lichens, able to support an exist- 

 ence, despite the fact that all the summer 

 they are baked quite dry, whilst during the 

 winter they are saturated with sea water. 

 What other plants could possibly sustain life 

 under such conditions ? In these little rocks 

 we have a very fair representation of the 

 character of the earth in those far-away times 

 when there was no covering of kindly soil to 

 provide a rooting medium for plants. 



In a broad way, we may say that the fungus 

 element of the alliance in the case of the lichen 

 is parasitic on the algce ; the fungus, in com- 



