92 THE ROOT. 



own, and, consequently, does not produce leaves. This economy 

 is, as it were, foreshadowed in the embryo of the Dodder, which 

 is a slender thread spirally coiled in the seed (Fig. 123, 124), and 

 which presents no vestige of cotyledons or seed-leaves. A spe- 

 cies of Dodder infests and greatly injures flax in Europe, and 

 sometimes makes its appearance in our own flax-fields, having 

 been introduced with the imported seed. Some species make 

 great havoc in the clover- fields of the Old World. 



136. Such parasites do not live upon all plants indiscriminately, 

 but only upon those whose elaborated juices furnish a propitious 

 nourishment. Some of them are restricted, or nearly so, to a par- 

 ticular species ; others show little preference, or are found indif- 

 ferently upon several species of different families. Their seeds, 

 in some cases, it is said, will germinate only when in contact with 

 the stem or root of .the species upon which they are destined to 

 live. Having no need of foliage, such plants may be reduced to a 

 stalk with a single flower or cluster of flowers, as in the different 

 kinds of Beech-drops,* the Cytinus, which is parasitic on the Cistus 

 of the South of Europe, &c. They may even be reduced to a 

 single flower directly parasitic on the bark of the foster plant, 

 without the intervention of any manifest stem. A truly wonderful 

 instance of this kind is furnished by that vegetable Titan, the Raf- 

 flesia Arnoldi of Sumatra (Fig. 125). The flower which was first 



discovered grew upon the stem of a kind of grape-vine ; it meas- 

 ured nine feet in circumference, and weighed fifteen pounds ! Its 

 color is light orange, mottled with yellowish-white. 



* See family Orolanchacece, in the second part of this work. 



FIG. 125. Rafflesia Arnoldi ; an expanded flower, and a bud, directly parasitic on the stem 

 of a vine : reduced to the scale of half an inch to a foot. 



