IX FILICINE^ LEPTOSPORANGIATJE 323 



divisions in the embryo, so that each octant may be said to 

 have a three-sided apical cell. When the octant wall in the 

 root quadrant is decidedly oblique this is not always evident in 

 the smaller octant, and the larger one in this case at once 

 becomes the definitive apical cell of the primary root. 



The first of these walls is usually parallel to the basal, the 

 second to the quadrant wall. Sometimes this order is reversed, 

 but never, apparently, is the first wall parallel with the octant 

 wall. Before the third segment is cut off from the octant, each 

 of the two first ones divides by a periclinal wall into an inner 

 and an outer cell. Each octant now consists of five cells, two 

 inner and three outer ones, of which one is the primary octant 

 cell, which still retains its original tetrahedral form. The 

 outer cell of each segment divides by a radial wall, but beyond 

 this the succession in the walls differs. Of the eight original 

 octants, one in each quadrant persists as the apical cell respect- 

 ively of cotyledon, stem, root, and foot, but in the latter it 

 becomes very early obliterated by the formation of a periclinal 

 wall and further longitudinal divisions, which is the case also 

 with one of the octants in the leaf and root. In the stem both 

 octants persist, one becoming the permanent stem apex, the 

 other forming the apical cell of the second leaf. 



Shaw ((2), p. 280) found in one instance an embryo in 

 which the first wall in the hypobasal part of the embryo was 

 the median wall instead of the usual transverse wall. 



The Cotyledon 



Of the two primary octants of the cotyledon, one very early 

 ceases to grow and soon becomes indistinguishable, and the 

 subsequent growth is due almost entirely to the activity of a 

 single octant. The apical cell is at first like that of the other 

 members, tetrahedral, but after about two sets of segments 

 have been cut off from it no more are usually cut off from the 

 side of the apical cell parallel to the basal wall, and the three- 

 sided cell thus passes over into a two-sided one with segments 

 cut off alternately right and left. By the suppression of the 

 growth in the sister octant, the apical cell gradually assumes a 

 nearly median position. By the change to the two-sided form 

 of the apical cell, the originally conical leaf rudiment becomes 

 flattened, and a little later this is followed by a dichotomy of 



