MORPHOLOGY OF THE EOOT. 



39 



ishment ready prepared, it. requires no proper digestive organs 

 of its own, and, consequently, does not produce leaves. This 

 economy is foreshadowed in the embryo of the Dodder, which is 

 a naked thread spirally coiled in the seed (Fig. 78, 79), and 

 presenting no vestige of cotyledons or seed-leaves. A species 

 of Dodder infests and greatly injures flax in Europe, and some- 

 times makes its appearance in our own flax-fields, having been 

 introduced with the imported seed. Such parasites do not live 

 upon all plants indiscriminately, but only upon those whose 

 elaborate juices furnish a propitious nourishment. 1 Some of 

 them are restricted, or nearly so, to a particular species ; others 

 show little preference, or are found indifferently 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 the}* are destined to live. Having no 

 need of herbage, such plants may be reduced to a stalk bearing 

 a single flower or a cluster of flowers, or even to a single blossom 

 developed from a bud directly parasitic on the bark of the foster 

 plant. Of this kind are the several species of Pilostyles (para- 

 sitic flowers on the shoots of Leguminous plants) in Tropical 

 America, one species of which was discovered by Dr. Thurber 



near the southern borders of New Mexico. Its flowers are 

 small, only about a quarter of an inch in diameter. The most 

 wonderful plant of this kind is that vegetable Titan, the Raf- 

 flesia Arnoldi of Sumatra (Fig. 80) which grows upon the stein 

 of a kind of a Cissus or Vitis. It is a parasitic flower, measuring 

 nine feet in circumference, and weighing fifteen pounds ! Its 

 color is light orange, mottled with yellowish- white. 



1 Monotropa or Indian Pipe (and perhaps some related plants), although 

 probably parasitic on living roots in early growth, appears to live afterwards 

 in the manner of the larger Fungi, upon leaf-mould and decaying herbage. 

 Its mode of life should be investigated. 



FIG. 80. 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. 



