HERB .1 G9 



CHAPTER XI. 



THE STEIkl, OR ASCENDING AXi;^. , , , , ,, ,. , 



161. That part of the plant wliich originates with the phim- 

 ule (124, b), and arises above the surface, expanding itself to 

 the influence of the air and the light, is called the ascending 



AXIS or STEM. 



a. The cause of its upward tendency is unknown (131, note), but is suppos^^ 

 to be in some way due to the principles of light and gravitation. , 



162. Altliough the first direction of the stem's growth is verti- 

 cal, there are many plants in wliich it does not continue so, but 

 extends in an oblique or horizontal direction, either just above 

 the surface of the ground, or just beneath it. When the stem 

 continues to arise in its original direction, it is said to be erect. 

 AVhen it grows horizontally upon the surface, it is said to be 

 prociimbeirt, creejnng, trailing, &c. "When it arises obhquely it 

 is an ascending stem, and when it continues buried beneath the 

 soil it is a suhterratiean stem. '-i 



a. Ilie subtciTancan stem, and some vaiieties of the creeping, have usually 

 been described as roots. 



163. In regard to duration, the stem, hke the root, is said to 

 be annual when it lives but one season, aftenvards dying, at 

 least down to the root, and ])erennial when its existence is con- 

 tinued beyond one season, to an indefinite period of time. 



164. In regard to the size and duration of the stem, plants are 

 distinguished into trees, shrubs, and herbs. 



a. A TREE is a plant with a perennial, woody stem, or trunk, 

 which does not divide into branches for a certain distance above 

 the ground. Ex. elm, palm. 



h. A SHR.UB is a plant of smaller dimensions than a tree, hav- 

 ing a perennial, woody stem, which divides into branches at or 

 near the ground, like the alder. A shrub of diminished size is 

 termed an under sliriib. Ex. whortlebeny. 

 y„c. An HERB is a plant ^vith aii amiual or perennial rppt, pro^^ 



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