70.] 



THE BOOT. 



88 



nourishment wholly from the air. The Long-moss 

 (Tillandsia) and Conopseum are examples. 



247, Old Oak trunk with horizontal branch bearing epiphytes and para- 

 sites, a, A fern (Polypodium incanum). b, Epidendrum conopseum. oc, 

 Long-moss (Tillandsia). d, Mistletoe (Viscum). e, Lichen. 



209. Parasites Three classes. Very 

 different in nature are the roots of 

 those plants called parasites, which feed 

 upon the juices of other plants or trees. 

 Such roots penetrate the bark of the nurse-plant to 

 the cambium layer beneath, and appropriate the stolen 

 juices to their own growth ; as the Dodder and Mistle- 

 toe. Other parasites, although standing in the soil, are 

 fixed upon foreign roots, and thence derive either their 

 entire sustenance, as the Beech-drops and other leaf- 

 less, colorless plants, or a part of their sustenance, as 

 the Cow-wheat (Melampyrum) and Gerardia. 



210. Subterranean stems. As there are aerial roots, so there are sub- 

 terranean stems. These are frequently mistaken for roots, but may be known 

 by their habitually and regularly producing buds. Of this nature are the 

 tubers of the Irish Potato, the rootstock of the Sweet-flag, the bulb of the 

 Tulip. But even the true root may sometimes develop buds accidentally as 

 it were in consequence of some injury to the upper axis, or some other 

 unnatural condition. 



