132 PARASITES. 
(page 45), placed over the true epidermis, to which the name of 
root-sheath (velamen radicunv) has been applied by Schleiden, 
who also calls such roots coated roots. . 
Besides these epiphytes, there is another very interesting class 
of plants which are called narasites : these we must now notice. 
Parasites.—These are plants which not only grow upon 
others, but which, instead of sending their roots into the air 
and deriving their food from it, as is the case with the epi- 
phytes, send them into the tissues of the plants upon which 
they grow, and obtain nutriment from them. The plant which 
they thus penetrate and feed upon is termed their host; and 
their sucking roots are termed haustoria. The Mistletoe (Vis- 
cum album), Broom-rapes (Orobanche), Dodders (Cuscuta) (fig. 
Fic. 2957. 
Fig. 258. 
Fig. 257. Cuscuta or Dodder-plant. 
Fig. 258. Flower and flower-bud 
of Rafiesia Arnoldi, a parasitic plant 
of Sumatra, 
257), and Rafflesia Arnoldi (fig.258), may be cited as examples 
of such plants. These parasites are of various natures: thus 
some have green foliage, as the Mistletoe ; while many others 
are pale, or brownish, or possess other tints than green, as the 
Broom-rapes and Rafflesia. The latter plant is especially inter- 
esting from its producing the largest flowers of any known 
plant : thus the first flower which was discovered measured nine 
feet in circumference, and weighed fifteen pounds. 
Parasitical plants also vary in the degree of their parasitism ; 
thus the Mistletoe and the greater number of parasites are, so 
far as their roots are concerned, entirely dependent upon the 
plants on which they grow for their food. Others, as the 
Dodders, obtain their food at first, like other plants, by means 
of the ordinary roots contained in the soil; but after having 
arrived at a certain age, these perish, and they then derive their 
food entirely from roots which penetrate the plants upon which 
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