Ch. IV, 21 



STRUCTURE OF STE.MS 



12; 



older, they were named exdogexous, and the name remains 

 in use. This tj-pe is characteristic of Grasses. Lihes, Palms, 







wmh!^n 







m 



Fig. S3. — Typical exogenous and endogenous stems, in cross section, of 

 Red Pine and a Palm : X j. iDrawn 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 

 tj'pes appears very clearly in our 

 picture (Fig. 83 1. The tT.-pical 

 endogenous t^-pe 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 illu.strate. 

 The great heights maintained by 

 such stems with slender diameters 

 rest partly on the }ielding elasticity permitted by the long 

 cur\dng courses of their separate fibro-vascular btmdles 



Pig. S4. — The Dragon Tree, 

 Draccena Draco, of the Canar\' 

 Islands, an endogenous plant 

 which grows indefinitely in diam- 

 eter. I From Balfour. I 



