Ch. IV, 2] 



STRUCTURE OF STEMS 



127 



older, they were named endogenous, and the name remains 

 in use. This type is characteristic of Grasses, Lilies, Palms, 





Fig. 83. — Typical exogenous and endogenous stems, in cross section, of 

 Red Pine and a Palm ; X £. (Drawn from photographs.) 



and in fact of all plants in the great natural group of the 

 Monocotyledons, where it is associated with parallel-veined 

 leaves, and sparse branching. 

 The contrast between the two 

 types appears very clearly in our 

 picture (Fig. 83). The typical 

 endogenous type does not permit 

 an indefinite increase in diameter, 

 for, after the fibro-vascular 

 bundles first laid down have in- 

 creased to their full size, the stem 

 no longer enlarges in diameter, 

 but only in height, whereby en- 

 dogenous plants are rendered 

 extremely slender and graceful, as 

 Palms and Bamboos illustrate. 

 The great heights maintained by which grows indefinitely in diam- 



, 6 . * . . .. . J eter. (From Balfour.) 



such stems with slender diameters 



rest partly on the yielding elasticity permitted by the long 



curving courses of their separate fibro-vascular bundles 



Fio. 84. — The Dragon Tree, 

 Dracaena Draco, of the Canary 

 Islands, an endogenous plant 



