VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEJE 253 



seen, entirely unbranched. Sections show that here, as in most 

 vascular plants, the growing point of the root is not at the apex, 

 but some distance below and protected by the root-cap. The 

 growth of the root in Ophioglossuin can be traced to a single 

 apical cell (Fig. 137), which is of large size, and, like that of 

 the stem, approximately pyramidal in form. While the divi- 

 sions show greater regularity than in the stem, still they are 

 very much less so than in the leptosporangiate Ferns. Seg- 

 ments are cut off not only from the lateral faces of the apical 

 cell, but also from its outer face. These outer segments help 

 to form the root-cap, which, however, is not derived exclusively 



Fig. i27.^0phioglossum pendulum. A, Longitudinal; B, transverse sections of 



the root apex, X215. 



from these, but In part also from the outer cells of the lateral 

 segments. Each of the latter is first divided by a nearly ver- 

 tical wall, perpendicular to its broad faces, into two "sextant 

 cells," but beyond this no regularity could be discovered in the 

 order of division in the segments, and the tissue at the growing- 

 point, especially in longitudinal section, presents a very con- 

 fused arrangement of the cells. A little lower down two 

 regions are discernible, a central cylinder (plerome), whose 

 limits are not very clearly defined, and the periblem or cortex. 

 A definite epidermis is not distinguishable. 



The first permanent tissue in the plerome cylinder or stele, 

 which is elliptical in section, arises in the form of small tracheids 



