CONIFERALES 267 



are continuous from this group to root cap, periblem, and plerome. Of 

 course, the root cap comes from the lower layer of meristematic cells, 

 and so it is said to come from the periblem. This single layer of cells 

 seems to form a mantle over the tip of the plerome, and, laterally, 



Fig. 272. — Pinus hanksiana: transverse section of young root, showing root hairs. 

 The root is diarch and secondary growth is beginning; X130. 



in the longitudinal section, it is continuous with the periblem. That it 

 gives rise to periblem and root cap seems to be a safe conclusion, but 

 whether some periclinal mitosis may not add a cell to the group 

 above is not so certain. Cells immediately above this single layer 



