i8o 



THE BOOK OF NATURE STUDY 



for the differences, and to interpret their past history by the 

 vegetation of the present time, are some of the problems now being 

 studied in what is known as Plant Ecology, that is, the study of 

 the habitats of plants. 



PARASITES 



Plants which live on other plants are known as Parasites ; 

 those which get their food from decaying leaves or wood, or any 

 part of a plant, are called Saprophytes. Amongst the Fungi, 

 Mosses, and Liverworts, both parasites and saprophytes 

 are found. Some Flowering Plants are also parasitic in habit. 

 The Broomrape, Dodder, Toothwort are true 

 parasites ; whilst the Cow-wheat, Bartsia, and 

 Eyebright are only partly parasitic, for they do 

 not derive their nourishment entirely from other 

 plants. The Toothwort is a plant without green 

 leaves, growing on the roots of Poplars and other 

 trees. The seed germinates on damp earth. If 

 the radicle in its growth meets with the living 

 root of an Ash, or Poplar, or Hazel, it fastens on 

 it at once, and develops a kind of sucker by which 

 it clings to its host. The seedling Toothwort 

 now begins to feed on its host, and grows 

 rapidly, producing fleshy scale-like leaves, which 

 overlap one another closely. The scaly stems 

 branch underground and may cover a square 

 yard. The flowers and leaves formed above the 

 ground have a purplish tinge, but no green 

 colouring matter. This is therefore a true para- 

 site. The Broomrape and Dodder also have no chlorophyll. 



The Cow-wheat, the Rattles, the Eyebright, and many other 

 plants belonging to the Scrophulariaceae, are only partially parasitic. 

 They have well-developed seedlings, and it is not until they have 

 reached a certain stage of development that they begin to prey 

 on other plants. Besides this, they have green leaves, and can 

 therefore use the carbon dioxide in the air. Many of these plants 

 are annuals, and occur by hundreds and thousands close together. 

 One has only to think of the Eyebright in pastures, of the Ycllow- 



FIG. 52. Toothwort 

 (Lathraasquamarid). 



