18 



MORPHOLOGY, OR COMPARATIVE ANATOMY. 



The nature of the root-hairs will be explained under the head of the 

 Anatomy of Roots. Examples may be found in seedling plants of 

 mustard, in potted Geraniums (Pelargonium), or in the roots of many 

 Monocotyledonous bulbous plants and Grasses growing in damp places. 



Media in which Roots grow. Eoots of ordinary plants bury 

 themselves in the soil ; those of water -plants, usually more succu- 

 lent in their texture, penetrate the mud, as in the Water-lilies, or 

 hang freely down in the water, as in Duckweed and the Water 

 Crowfoot. A number of plants exhibit what are called aerial 

 roots, which are always adventitious ; and these may be either the 



Fig. 9. 



Sketch of a Mangrove-tree (lihizophora), with true roots descending from the branches. 



sole radical organs of the plant, or roots developed high above the 

 ground but growing down to reach the soil, or they may be con- 

 verted into organs of support for a weak stem. In true parasitical 

 plants, like the Mistletoe, the roots, more or less developed, attach 

 themselves to, and become organically blended with, the roots or 

 stems of other plants. 



The plants called epiphytes, such as the aerial Orchids, various Araceous 

 plants, and members of the Pine-apple family, are possessed of aerial roots 

 alone. The stem of such plants rests upon some foreign body, such as the 

 branch of a tree, totally unconnected with the earth, and produces long 

 adventitious roots which hang suspended in the atmosphere. Roots 



