286 CONSERVATIVE ORGANS. [LECT. VII. 



Palms affords examples of the first description of 

 ligneous stems, and all other trees of the second. 

 As far as respects substance, however, ligneous 

 stems are not arranged according to the diversity 

 of structure I have just hinted at ; but according 

 to the degree of cohesion which binds together 

 their ligneous fibres. Botanists have, therefore, 

 divided woody stems into two genera, the solid 

 and the fibrous. 



1 . The solid woody stem (C. solidus) is that 

 in which the cohesion is uniform, and the 

 wood, consequently, compact and indurated; 

 sometimes to a degree on which the knife will 

 make scarcely any impression. 



2. The fibrous (C.fibrosus) is that in which, 

 the cohesion being irregular, the wood is con- 

 stituted of fibrous bundles ; which, although 

 adhering to each other, can be easily separated, 

 either by tearing or by maceration. 



Ligneous stems of every description are peren- 

 nial. 



B. HERBACEOUS stems (Caules herbacei) are 

 those which contain a small proportion of woody 

 matter ; but are composed chiefly of cellular sub- 

 stance, and consequently can be easily cut or 

 divided. There are three distinct kinds of her- 

 baceous stems: the fleshy^ the spongy, and the 

 hollow. 



