150 MORPHOLOGY 



pith), but is made up of collateral bundles (p. 146), separated from one 

 another by pith rays (radiating plates of tissue extending from pith to 

 cortex). This is the general structure of the vascular cylinder of the 

 majority of seed plants, and this resemblance is further emphasized 



FIG. 352. General habit of Ophio- 



glossum. After SACHS. FIG. 353. General habit of Botrychium. 



bv the presence of a cambium cylinder (a meristematic tissue between 

 the xylem and phloem that adds new elements to both). This means 

 increase in diameter by the formation of secondary wood (xylem), and 

 among the elements of this secondary wood there appear tracheids with 



