INFLUENCE OF ENVIRONMENT 279 



case of such complete parasites as the dodder (Cuscuta) 

 or the gigantic Rafflesia of Sumatra, the plants are quite 

 destitute of chlorophyll and completely dependent upon 

 the host for their nourishment. In these the leaves are 

 reduced to scales, and the plant sends root-like suckers 

 into the host, or, in the case of Rafflesia and some re- 

 lated plants, the whole vegetative part of the parasite 

 lives within the host, like a fungus, and only the 

 monstrous flowers are borne upon the outside. 



Similar in appearance to these parasites are a number 

 of saprophytic plants which get their nourishment 

 mainl} 7 from the decaying organic matter in vegetable 

 mould or humus. Both leaves and roots in these plants 

 are imperfectly developed (Fig. 59, C), and in some 

 cases, at least, in common with many other plants, they 

 are intimately associated Avith a fungus in the soil 

 which seems to supply them with the food elements 

 derived from the organic matter in the earth. The 

 curious Indian pipe (Monotropa) and its more showy 

 relation, the crimson snow plant (Sarcodes) of the 

 Sierra Nevada, are examples of these humus plants. 

 In all these parasites and saprophytes there is a marked 

 degeneration of the assimilating organs, and this often 

 extends to other parts of the plant, including the ovules 

 and embryo. 



SYMBIOSIS 



A curious association of two plants together, or less 

 often of a plant and animal, is a not uncommon occur- 

 rence, this "symbiosis' being apparently mutually 

 beneficial, although sometimes it looks more like a case 

 of parasitism. A number of liverworts, e.g. Blasia, 



