Px\RASITES AND SEMIPARASITES 219 



plants — the hosts, as they are called — and draw from 

 them the whole or part of their nourishment. The 

 Dodder is a familiar instance of a plant wholly 

 parasitic on Thyme and a variety of other hosts. 

 The Mistletoe is a semiparasite. It attaches itself 

 to the branches of the Apple and some other 

 trees, and while it draws part of its nutriment 

 from the host, yet, by means of its leaves, it manu- 

 factures a portion, at least, of its food-supply itself. 

 In the Alps pcirasites of either type are rare, with 

 the exception of the members of the order Scrophu- 

 lariacea3 mentioned above. 



Euphrasia and the other related genera are semi- 

 parasitic on the roots of Grasses, which they rob of 

 part of their food-supply. If we dig up a Lousewort, 

 and separate the plant from the tm^f very carefully, 

 we shall find that its roots are often attached to those 

 of certain Grasses. At the same time, these plants, by 

 means of their leaves, manufacture a portion of their 

 nutriment. 



