vii PTERIDOPHYTAFILICINE&OPHIOGLOSSACEJE 267 



ria shows even greater regularity in the arrangement of the 

 apical meristem than is found in B. Virginianum. A careful 

 examination of this point is much to be desired. 



The first wall in the young lateral segment is the sextant 

 wall, as in the higher Ferns, and divides the segment into two 

 cells of unequal depth. The next wall divides the larger of 

 these cells into an inner and an outer one, the former becoming 

 tl]e initial of the central plerome cylinder, the outer one, to- 

 gether with the whole of the smaller semi-segment, giving rise 

 to the cortex, in which the divisions are very similar to, but 



FIG. 147. Tetrarch vascular bundle of the root of B. Virginianum, X8s; en, endo- 

 dermis; ph, phloem; x, xylem. 



somewhat less regular than in Equisetum and the leptospo- 

 rangiate Ferns. As usual in roots of this type, segments are 

 also cut off from the outer face of the apical cell, but I have never 

 seen, either in B. Virginianum or B. ternatum, any indica- 

 tion that the growth of the root-cap was due exclusively to the 

 development of these segments, as Holle states both for B. 

 lunaria and Ophioglossum vulgatum. In both species of Botry- 

 chium examined by me the growth of the root-cap was evidently 

 due in part to the division of cells in the outer part of the lateral 

 segments, so that in exactly median sections there was not the 



