248 



MOSSES AND FERNS 



CHAP. 



of such forms as B. simplex will show an approximation to the 

 condition found in Ophioglossum, although Holle's ^ figure of 

 B. lunaria shows even greater regularity in the arrangement of 

 the apical meristem than is found in B. Virginianuni. 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 the 

 initial of the central plerome cylinder, the outer one, together 

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



Fig. 127. — Botrychium Virginianum (Sw.). A, Longitudinal ; B, transverse sections of the root apex, 



X 200 ; pi, plerome. 



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

 what less regular than in Equisetuni and the leptosporangiate 

 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 indication 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 

 Botrychium 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 



1 Holle (I). 



