PARASITISM 293 



in England and parts of Southern Scotland; it is very 

 rare in Ireland. It is found in Europe and North Asia, 

 also in North America; in Southern Europe it is an 

 alpine. Some forest trees, such as Pines, and also 

 Heaths, which flourish in an acid humus soil, are served 

 by subject-fungi, and thus are to some extent sapro- 

 phytic through their agency. In the course of time they 

 may become total saprophytes — a not over-glorious issue. 



Parasitism in plants is in many instances complete, 

 in others only by way of becoming complete. Parasitic 

 plants are interesting as indicating the length to which 

 plant-life will go in its determination to exist; but they 

 also " point a moral " in which the example elicits a 

 degree of contempt. A parasite lives at the expense of 

 another, doing no worthy labour, but always managing 

 to propagate its degenerate kind. In Britain we have 

 several plants which are developing vicious habits. These 

 are the Cow- wheat {Melampyrum), Lousewort {Pedicu- 

 laris), Eye- bright (Euphrasia), Bartsia, Yellow-rattle 

 {Rhinanthus) , and Bastard Toadflax (Thesium humi- 

 fosum). These all flourish among grass, and send out 

 root-processes into the roots of grasses, tapping them 

 for water, and also securing foodstuffs in solution in the 

 water. Indeed, they have taken the first step in the 

 direction of total parasitism, but as yet they do honest 

 work in manufacturing carbohydrates. The Mistletoe 

 is a partially parasitic epiphyte. We can reahze the 

 temptation of an epiphyte; there it is perched on a tree; 

 why should it not tap the tree for food ? The Mistletoe 

 has managed to do so ; but it still does something in the 

 manufacture of carbohydrates. 



