506 



BOTANY 



incapable of utilizing the carbon-dioxide of the atmosphere, and are 

 therefore either saprophytes or parasites. 



Among the higher plants there are also numerous examples of 

 such parasitic or saprophytic forms, which differ from their green 

 relations in being more or less completely destitute of chlorophyll. 

 Where the chlorophyll is quite absent, as in Cuscuta (Fig. 474), 

 Monotropa, Barcodes, etc., the leaves are reduced to inconspicuous 

 scales, and the roots may be absent as well. These plants may be ' 



FIG. 474. Cuscuta Gronovii. A parasite. (After BAILEY.) 



parasites e.g. Cuscuta, Epiphegus ; or they may be saprophytes, 

 e.g. Monotropa (Fig. 475), Corallorhiza. The latter are "humus 

 plants," i.e. they grow in earth composed largely of leaf mould, from 

 which they derive their nourishment. There are certain plants 

 which may be called semiparasites, for while they possess chloro- 

 phyll, and can therefore assimilate carbon-dioxide, nevertheless they 

 penetrate the tissues of other plants and take food from them. The 

 Mistletoe and various other Loranthaceae belong to this category; 

 and various species of Gerardia and other Scrophulariaceae attach 



