PARASITIC PLANTS. 91 



other hand, imperfect root-parasites with green foliage have re- 

 cently been detected in more than one tribe of plants ; * thus ex- 

 hibiting intermediate states between the Green and the 



135. Pale or Colored Parasites, that is, of other colors than 

 green ; such as Beech-drops, Orobanche, &c. These strike their 

 roots, or sucker-shaped discs, into the bark, mostly that of the root, 

 of other plants, and thence draw 

 their food from the sap already elab- 

 orated (79). They have according- 

 ly no occasion for digestive organs 

 of their own, and are in fact always 

 destitute of green foliage. In some 

 cases of the kind, as in the Dodder 

 (Fig. 122- 124), the seeds germinate 

 in the earth, from which the primi- 

 tive root derives its nourishment in 

 the ordinary manner ; but when the 

 slender twining stem reaches the 

 surrounding herbage, it gives out 

 aerial roots, which attach themselves 

 firmly to the surface of the support- 

 ing plant, penetrate its epidermis, 

 and feed upon its juices ; while the 

 original root and base of the stem perish, and the plant has no 

 longer any connection with the soil. Thus stealing its nourish- 

 ment ready prepared, it requires no proper digestive organs of its 



* In England a Thesium was discovered by Mr. Mitten to attach its roots 

 parasitically, by suckers, to the roots of adjacent herbs. (It would be inter- 

 esting to know if this is the case with our Comandra.) Then Decaisne, recol- 

 lecting that Rhinanthaceous plants generally, all of which blacken more or 

 less in drying, were known to be uncultivable, and have the reputation, in 

 France and elsewhere, of being injurious to cereal and other plants in their 

 vicinity, was led to the discovery that plants of Rhinanthus, Melampyrum, 

 and of the allied genera, attached themselves by numerous suckers on their 

 roots to the roots of Grasses, shrubby plants, and even of trees, among which 

 they grow. Our handsome species of Gerardia are equally uncultivable, 

 doubtless on account of this partial parasitism. 



FIG. 122. The common Dodder of the Northern States (Cuscuta Gronovii), of the natural 

 size, parasitic upon the stem of an herb: the uncoiled portion at the lower end shows the mode 

 of its attachment. 123. The coiled embryo taken from the seed, moderately magnified. 124. The 

 same in germination; the lower end elongating into a root; the upper into a thread-like leaf- 

 less slem. 



