SECT. II 



PHYSIOLOGY 



225 



and its light yellow, reddish-brown or amethyst-coloured flower-shoot appears 

 above the surface of the ground. Orobanche, like Cuscuta, contains a small 

 amount of chlorophyll. Both are dreaded pests ; they inflict serious damage upon 

 cultivated plants, and are difficult to exterminate. 



Many exotic parasitic plants, especially the Rafllesiaceae {^^), have become so 

 (completely transformed by their parasitic mode of life that they develop no 



Fio. 197. —Branch of a leguminous jilant from the surface of which the flowers of a parasitic 

 plant {Pilostyles Ulai, Solms) are protruding. (From Goebel's Organography.) 



apparent vegetative body at all ; but grow altogether Arithin their host plant, 

 whence they send out at intervals their extraordinary flowers. In the case of 

 Pilostyles, a parasite which lives on some shrubby Leguminosae, the whole 

 vegetative body is broken up into filaments of cells which penetrate the host 

 plant like the mycelium of a fungus. The flowers alone become visible and 

 protrude from the stems and leaf-stalks of the host plant (Fig. 197). 



In contrast to these parasites, which have come to be absolutely dependent 

 upon other plants for their nourishment, there are certain parasites which, to 

 judge by external appearances, seem to be quite independent, for they possess 



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