STRUCTURAL BOTANY. 



41 



circumference of tlie stem the bark will accumulate, wher- 

 ever leaves are formed. Exogens have a camhiuin 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 Exogens 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 Endogens 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. 



Pkincipal Kinds of Stems, not including TJndeegkound 



Stems. 



83. Stems are distinguished into triin'ks^ herbaceous 

 sterns^ scajpes and culms, 



'branchinff above tree, arbor. 



the younger branches 



becoming ligneous 



and persistent shrub, frutex. 



the younger branches 



dying every year ; 



plant commonly not 



higher than 1 to 3 



feet suffruticose plant, under shruh. 



flowering 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 Uennial. 



blossoming year after year, 



but dying down to the 



ground annually perennial. 



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). 



TrnnJc 



ligneous 



(with harder 



wood) 



Stem 

 herbaceous 



(caulis) 



witli softer 



wood 



branching 



also 



below 



