8TBUCTUBAL BOTANY. 



41 



circumference of the stem tlie bark will accumulate, wher- 

 ever leaves are formed. Exogens have a cambium, layer 

 — that is, a stratum of nascent wood and nascent bark 

 between liber and wood ; Endogens have none. The 

 wood-bundles of Endogens are therefore limited, and the 

 wood-wedges of the Egogens unlimited in growth. 



While EXOGENOUS stems have the oldest and hardest 

 wood at the centre, and the newest and softest at the cir- 

 cumference, in Entogens the wood is softest toward 

 the centre, and most compact at the circumference. 

 Their stems increase in diameter in consequence of the 

 continued deposition of new woody bundles so long as the 

 more or less complete outer rind is distensible. 



Peincipal Kinds of Stems, not iNCLuomG TlNDEEGEOtrND 



Stems. 



83. Stems are distinguished into trunks, herbaceous 

 stems, scapes and cuhns. 



branching above tree, arbor. 



the younger branches 



becoming ligneous 



and persistent shrii), frviex. 



the younger branches 



dying every year ; 



plant commonly not y 



higher than 1 to 3 



feet svffritticose plant, undershrub. 



flovirering and ripening its 



seed in the first year, and 



then dying, root and all annual. 



flowering in the second year, 



and dying, root and all, after 



ripening its seed hiennial. 



blossoming year after year, 



but dying down to the 



ground annually 



Trunk 



ligneous 



(with harder 



wood) 



herbaceous 

 (caulis) 



with softer 

 wood 



branching 



also 



below 



Scape : a peduncle springing from the root, leafless, or only with 

 bracts, and bearing a solitary, or several to many flowers (a spathe is 

 also a bract). 



