SPERMATOPHYTES 
24Q 
FIG. 555. Partly diagrammatic transverse section of vascular cylinder of root of 
Ranunculus: the two outermost layers belong to the cortex, the inner one being the 
endodermis; the next layer (outermost one of the stele) is the pericycle^ in the center is 
the group of xylem vessels, extending in four rays to the peri cycTej^theT outermost xylem 
vessels of each ray are protoxylem, the metaxylem having developed towards the center 
in four converging lines; between the xylem rays are the four groups of phloem (shaded). 
\^^ ^^ 557 556 
FIGS. 556, 557. Diagrams to show secondary thickening in root, 556 being the 
primary condition, 557 the secondary; x, primary xylem; p, primary phloem; c, cam- 
bium: n*, secondary xylem; np, secondary phloem. After COULTER. 
