EXTERNAL APPEx\EANCE. 17 



the beauty of their form and structure, and we shall now 

 proceed to examine in brief detail the general appearance 

 of the various organs of which they are composed. These, 

 as in more perfect plants, are stems, leaves, roots, etc., 

 which may be traced throughout the whole family, though 

 in several cases their presence is with difficulty detected. 



Commencing with the Hoots, we have previously remarked 

 that these arc in general very small and microscopic ; those 

 with the strongest being some of the largest Bnjums, grow- 

 ing on the ground, and those with the smallest, the various 

 minute Hijjinmns, or other genera with trailing stems of a 

 similar habit. In Ortliotriclium, and some others growing 

 exclusively on rocks or trees, the root is often a mere 

 flattened disc for the purpose of attacliing the plant to its 

 resting-place, while its nourishment is derived principally 

 from the atmosphere. The number of roots in some genera 

 and species makes up for their minuteness, as in Bartramia 

 arcuafa, where the brown masses of root — or what is sup- 

 posed to be so — sometimes become so luxuriant as to 

 smother entirely the stems and foliage. As may be ex- 

 pected, some of the trailing species make roots readily at 

 each joint of the stem, while others, of which Hookeria 

 lucens is an example, emit rootlets from every point of their 



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