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. 
by 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 
