LESSON 18.] THE ENDOGENOUS STEM. 51 



LESSOJST XYIII. 



THE ENDOGENOUS STEM. 



299. Endogenous stems have no separable bark; no distinct con- 

 centric circles ; the vascular circles are progressive and definite, the 

 solidity diminishing from the circumference to the centre ; no dis- 

 tinct pith ; no medullary sheath nor medullary rays ; the cellular 

 tissue being interposed between the vascular bundles. 



300. For the full development of the Endogen we must seek hot 

 climates, there it is that its peculiar mode of growth is seen in per- 

 fection. The palms and screw pines offer the best examples; the 

 former have simple, unbranched, cylindrical stems, attaining to a 

 great height, and covered by a large mass of remarkable foliage. 



301. The peculiar structure of this order of plants, will be best 

 seen by reference to the accompanying figures; the first (Fig. 87, A), 



Fio. 87. 



Monocotyledonous stem. 



is a transverse, and the second (B), a longitudinal section of the 

 same stem ; the letters in both refer to the like structures. 



302. In its early state the Endogenous stem consists entirely of 

 cellular tissue ; but as it increases in age, vascular bundles are pro- 

 duced, and these consist of woody fibre, spiral, dotted, and lactiferous 

 vessels. 



303. The cellular tissue (a, a, a, a) is here seen distributed 



