XII 



EQUISETINEJE 



455 



a different interpretation, and to judge from them it is quite as 

 likely that the root is hypobasal as in the other species examined. 

 The first two divisions in the stem quadrant estaljHsh the defini- 

 tive apical cell, which occupies nearly the centre of the epibasal 

 part of the eml)ryo, and is surrounded by a circle of fovu' cells, 

 two of which lielong to the leaf cjuadrant (Fig. 225, C), and two 

 are segments of the stem quadrant, the first one corresponding 

 morphologically to the second leaf of the Fern embryo. This 



Fig. 265. — A, An advanced embryo of E. arvense, surface view, X360; B, optical 

 section of a similar stage of E. palustre, X360; older embryo of E. arvense, X160; 

 St, stem; R, root (all the figures after Sadebeck). 



circle of cells forms the first sheath about the stem of the young 

 sporophyte. After one set of lateral segments has been cut off 

 from the root quadrant, the primary cap cell is formed as in the 

 Ferns. Unlike the latter, the divisions in the stem apex proceed 

 rapidly, and it soon projects in the centre of the embryo as a 

 broad conical prominence, terminating in the large tetrahedral 

 apical cell. 



The three parts of which the primary leaf-sheath is com- 

 posed remain distinct and form the three teeth (Fig. 265, C), 

 which grow rapidly until they are about on a level with the 

 apex of the stem. This growth is mainly due to the activity 

 of the marginal cells. The root grows less actively at first than 

 either stem or leaves, and at the time the latter is nearly fully 

 developed forms but a small protuberance at the base of the 

 embryo (Fig. 265, C). The foot at this time is not conspicu- 



