280 CONSERVATIVE ORGANS. [LECT. VI. 



characterized by its ligneous structure, by being 

 always perennial ; generally naked at the lower 

 part; and divided and subdivided towards the 

 summit into branches and twigs, bearing leaves 

 and the fructification. It is thickest at the base, 

 and gradually diminishes to the apex ; is covered 

 with a thick, often dry and cracked bark ; and 

 internally is composed of a central pith, sur- 

 rounded by ligneous layers, the number of which 

 varies according to the age of the plant. When 

 it rises to a moderate height, like a simple 

 column, before it divides into, or gives off 

 branches, it is said to be arboreous, as exemplified 

 in the Oak, the Elm, and the majority of trees ; 

 but when the divisions or branches occur near to 

 the soil, it is termed shrubby, fruticosus ; as in 

 the Lilac, the Rosemary, and such-like. These 

 terms, however, are always to be understood as 

 having a relative signification only; for various 

 circumstances, such as change of soil, climate, 

 and the efforts of art, may metamorphose shrubs 

 into trees, or reduce these again into shrubs; 

 transitions which are by no means uncommon. 



2. STALK (Caulis) is properly applicable to the 

 stems of herbaceous plants only ; although the 

 term is frequently used in a sense synonimous 

 with trunk. The specific characteristics of the 

 stalk are, that it is rarely ligneous, and lives but 



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