PLANTS OF THE MOORLAND 89 



succeed well where most other plants fail. The first 

 part of the answer is that heather plants are very 

 resistant to exposure. Their stems are wiry and their 

 leaf-surface is much reduced. In the Heather the 

 leaves are only about a quarter of an inch long; they 

 are closely packed in four rows. In the Heath the 

 outer margins are turned back, and screen the lower 

 surface, on which there are the little openings (or 

 stomata) through which transpiration of water takes 

 place. This is well adapted for life on exposed areas, 

 scorched by the sun in summer and swept by the wind 

 at every season, where there has to be economy with 

 water. Even when there is a heavy rainfall and plenty 

 of water on the heather-covered moorland, this is apt 

 to be in an acid state which the roots cannot readily 

 utilise. 



The second part of the answer is rather unex- 

 pected; it concerns the roots. It is not merely that 

 these are long and travel far, as you will see on trying 

 to pull one up; it is that they have entered into part- 

 nership with a Fungus. The outer surface of the 

 young root of the Common Heather bears no root 

 hairs, but is covered with the transparent threads of 

 a Fungus. These threads or hyphae enter the root 

 and coil in its cells; they grow into stem and leaves; 

 they penetrate even into the ovary of the flower; they 

 infect the envelopes of the seed. Perhaps the Fungus 

 was a parasite to begin with, but it has become a 

 partner. It probably enables the Heather to utilise 

 the organic matter that there is in the soil when peat 

 begins to form, and perhaps it enables the Heather 

 to utilise the free nitrogen of the air, just as is done 

 by the bacteria in the root tubercles of leguminous 



