IRREGULAR NUTRITION 



189 



partial parasites. This state is seen in the Loranthaceae, with the 

 familiar example of the Mistletoe (Viscum), a plant which grows fixed 

 on the branches of various trees. It occurs occasionally on the Oak, 

 on which it was in early days recognised as the mysterious " Golden 

 Bough." Other native green parasites are the Eyebright (Euphrasia 

 officinalis), and the Yellow Rattle (Rhinanthus crista-galli), while 

 Cassytha, a very omnivorous parasite of the tropics, has also a green 

 colour. 



These plants are all fixed by means of haustoria or suckers upon the 

 host-plant in such a way that the tissues of the one come into close 

 relation with the tissues of the other. In the case of Eyebright and 



FIG. 140. 



Root of Louse-wort (Pedicularis), which like Eyebright and Yellow-Rattle, is fixed 

 by suckers upon the roots of the host, here represented black. (After Maybrook.^ 



illow Rattle there are suckers upon the roots, and they penetrate 

 roots of the grasses with which the plant grows. The close juxta- 



isition of the roots in the sod offers a ready opportunity for the 

 parasite (Fig. 140). The effect of the parasitism upon the Grasses in 

 a meadow is such that patches infested by Yellow Rattle can often be 

 recognised from a distance by the poverty of their growth. In 

 Cassytha the suckers arise from the shoot, and the close vegetation of 

 the tropical undergrowth gives the necessary contact at many points. 

 In the case of Mistletoe, and of its near relative Loranthus, the 

 opportunity for parasitic attachment arises from the fact that their 

 fruits are viscid ; in fact Bird-Lime is derived from them. The berries 

 are eaten by birds which reject the sticky seeds, leaving them attached 

 to the twigs on which they perched. Here the seeds germinate, and 

 their roots penetrate the living tissues of the host. In Viscum a 



