122 THE SCIENCE OF LIFE. 



CHAPTER IX. 



ENDOGENS. 



What time this world's great workmaister did cast 

 To make all things such as we now behold, 

 It seems that He before His eyes had plast 

 A goodly patterne, to whose perfect mould 

 "Tie fashioned them as comely as he could, 

 That now so fair and seemly they appear 

 As naught may be amended anywhere. 



SPENSER. 



I. ENDOGENOUS plants have no separable bark, nor 

 distinct concentric circles in the stem. Their fibro- 

 vascular bundles, consisting of spiral and porous vessels 

 and woody fibers, descend from the leaves downward, 

 converging at first toward the center, but afterward di- 

 verging outward until they reach the roots, or attach 

 themselves to the hardened tissue of the outer or corti- 

 cal layer, corresponding to the bark in Exogens, but 

 harder than the rest of the stem, and inseparable from 

 it. It used to be thought that the woody portion was 

 added to the center, and pushed the first-formed fibers 

 toward the circumference; hence the term Endogenous, 

 (endon, within, and gennao, to produce.) In strict scien- 

 tific accuracy the term only applies to the fibers at the 

 early part of their course, since in the latter part they 

 become blended in the cortical layer, forming a tough 

 net-work. The center of the stem when young is filled 

 with cells which sometimes disappear, except at the 

 nodes, leaving the stem hollow, as in Grasses. 



