182 THE BOOK OF NATURE STUDY 



to a bird's nest. The Coral-Root has an underground stem, some- 

 what like the tangled roots of the Bird's-Nest, but it has no true 

 root ; the rhizome branches, forming a mass not unlike a piece of 

 coral. Every year pale greenish shoots arise from the underground 

 stem, bearing small flowers with a scent suggestive of vanilla; later, 

 green fruits develop and turn brown when they ripen. This 

 Orchid belongs to E. Scotland. It must not be confused with 

 another plant, also called Coral-Root, which belongs to the Cruci- 

 ferae and is not a saprophyte. Many other plants, especially 

 in moorland regions, are saprophytic in habit. The Moor Mat- 

 grass (Nardus stricta), some Sedges and Rushes, certain Gentians 

 are instances of this. When these plants are taken up from their 

 natural habitat and planted in a garden they usually live only for 

 a short time, even though the clods of peat in which their roots 

 are imbedded are transplanted with them. It is supposed, 

 therefore, that the organic compounds formed by the decaying 

 vegetable matter differs in character under the different conditions 

 of temperature and moisture which obtain on a moor and in a 

 garden. 



ASSOCIATIONS OF PLANTS IN THE SAME HABITAT 



Plants which differ from each other in many respects may yet 

 be associated together in the same habitat, if similar conditions 

 of light, moisture, wind, etc. suit them. Thus it has been shown 

 that certain plants belong to woods ; these would not be found 

 on sea-cliffs or on exposed commons, where there would not be 

 enough shade or moisture for them. From this point of view 

 all plants may be arranged in three or four well-marked groups : 



1. Hydrophytes. These comprise all aquatic plants, whether 

 entirely or partially submerged, provided that there is not less 

 than 80 per cent, of water in the soil. 



2. Xerophytes. These include rock, desert, and moor plants 

 which like a soil with less than 10 per cent, of water. With this 

 group may be associated those plants that will tolerate salt in the 

 soil; these are found on sand-dunes, and are known as Halophytes. 



3. Between the Hydrophytes and Xerophytes come those 

 plants which like a regular rainfall and a soil more or less rich 

 in humus. These are called Mesophytes. The vegetation of our 



