LAVA -FLOWS 



plants. Yet even then there were no trees, and there was no 

 continuous mantle of green plants such as we are accustomed 

 to in this country. He also found many plants growing on 

 the lava which are generally found on the branches of trees, 

 that is, which can do without a thick layer of soil. He also 

 found quantities of a pitcher plant. Nepenthes (which lives 

 mainly on insects caught in its pitchers). 



This does not at first sight seem to agree at all with what 

 has been given for the walls. It is true that sometimes in the 

 Highlands, or Lowland and Lakeland Hills, one comes across 

 quantities of the Bladderfern and others growing on the 

 " screes." (These last may be described as streams of broken, 

 angular stones, filling small gullies, and spreading out at the 

 base over a considerable space.) Often these ferns seem to 

 be all that can thrive in amongst the stones. But in a mild 

 and temperate country like our own, one would expect 

 things to proceed differently. 



And in fact they do so. Every one must have noticed a 

 green stain which covers wet walls, stones, stucco, even 

 marble statues, and especially tree bark in wet or damp 

 situations. This is a minute green seaweed rejoicing in the 

 name of Pleurococcus. It is a pretty object for the micro- 

 scope. 



This, of course, is the first stage of colonization. It is 

 followed by mosses of sorts. 



But there is a more interesting series still in a climate 

 resembling our own. The iava-flows from Mount Vesuvius 

 have been investigated by several observers. 



There it was found that the first inhabitants were lichens 

 and small green seaweeds ; then " different mosses occupied 

 the lava over which a certain quantity of vegetable dust had 

 been scattered.**' After this, scattered ferns and even small 



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