SECTION 5.J ROOTS. 37 



upon the trunks or limbs of other plants ; by the latter because, having no 

 connection with the soil, they must derive their sustenance from the air 

 only. They have aerial roots, which do not reach the ground, but are used 

 to fix the plant to the surface upon which the plant grows : they also take 

 a part in absorbing moisture from the air. 



80. Parasitic Plants, of which there are various kinds, strike their 

 roots, or what answer to roots, into the tissue of foster plants, or form atr 

 tachmeuts with their surface, so as to prey upon their juices. Of this sort 

 is the Mistletoe, the seed of which germinates on the bough where it 

 falls or is left by birds ; and the forming root penetrates the bark and en- 

 grafts itself into the wood, to which it becomes united as firmly as a natural 

 branch to its parent stem ; and indeed the parasite lives just as if it were 

 a branch of the tree it grows and feeds on. A most common parasitic herb 

 is the Dodder; which abounds in low grounds ia summer, and coils its 

 long and slender, leafless, yellowish stems resembling tangled threads of 

 yarn round and round the stalks of other plants ; wherever they touch 

 piercing the bark with minute and very short rootlets in the form of 

 suckers, which draw out the nourishing juices of the plants laid hold of. 

 Other parasitic plants, like the Beech-drops and Pine-sap, fasten their roots 

 under ground upon the roots of neighboring plants, and rob them of their 

 juices. 



81. Some plants are partly parasitic ; while most of their roots act in 

 the ordinary way, others make suckers at their tips which grow fast to the 



roots of other plants and rob them of nourishment. Some of oar species of 

 Gerardia do this (Fig. 89). 



82. There are phanerogamous plants, like Monotropa or Indian Pipe, 

 the roots of which feed mainly on decaying vegetable matter in the soil. 

 These are SAPROPHYTES, and they imitate Mushrooms and other Fungi in 

 their mode of life. 



83. Duration of Roots, etc. Roots are said to be either annual, bien- 

 nial, or perennial. As respects the first and second, these terms may be 

 applied either to the root or to the plant. 



84. Annuals, as the name denotes, live for only one year, generally for 



PIG. 89. Roots of Yellow Gerardia, some attached to and feeding on the root ol 

 * Blueberry-bush. 



