THE VASCULAR CRYPTOGAMS 



105 



a.c. 



L 



already assumed the pyramidal form which it keeps 

 all through life. 



In the mean -time similar divisions have taken 

 place in the lower half of the young embryo. Here 

 an inclined wall separates the cell destined to give 

 rise to the main root from one which merely forms the 

 foot, a comparatively unimport- 

 ant structure in Equisetum. 

 The root-cell, which lies ex- 

 actly opposite that from which 

 the stem is derived, divides up 

 so as to form the usual pyra- 

 midal apical cell, from which, 

 by a wall parallel to the free 

 surface, the root-cap is marked 

 off. Thus the young embryo 

 of Equisetum is started, and even 

 at this early stage shows some- 

 thing of the characters of the 

 mature plant, such as the 

 whorled leaves and pyramidal 

 apical cells. Fig. 47 shows a 

 very young embryo enclosed in 

 the venter of the archegonium, 

 when only a few divisions have 

 taken place. In Fig. 48 we see the section of an embryo 

 at a much more advanced stage, when two whorls of 

 leaves are already formed. 



Up to about this age the embryo remains within the 

 cavity of the enlarged archegonium. So far, the root 

 has not developed much, but now it grows rapidly and 

 breaks through the tissue of the prothallus below it. 

 It is followed by the stem, which bursts the neck 



FIG. 48. Equisetum maxi- 

 mum ; embryo in median 

 longitudinal section, a.c, 

 apical cell of stem ; 1 1} leaf 

 of first whorl ; I 2t leaf of 

 second whorl ; r, root. 

 Magnified about 200 dia- 

 meters. (After Buchtien.) 



