

vii PTERIDOPHYTAFILICINE&OPHIOGLOSSACEJE 243 



The subsequent divisions apparently show great irregu- 

 larity, and the embryo does not exhibit the early development 

 of apical initial cells so marked in the typical Ferns. 



The whole epibasal part of the embryo is devoted to the for- 

 mation of the foot, in this respect showing an analogy, at least 

 with Anthoceros. From the epibasal region arise the shoot and 

 the root, both of which later develop a definite apical cell. The 

 initial cell of the root at once begins to form periclinal cells, 

 which cut off the segments of the root cap from its outer face, 

 and the apical cell thus becomes deeply sunk beneath the surface 

 of the root-apex, which projects but little beyond the other parts 

 of the very massive embryo-sporophyte. The primary leaf, or ( 

 cotyledon (Fig. 130 cot.), unlike that of the true Ferns, arises 

 secondarily from the shoot. 



In one instance, Jeffrey found small tracheids present in a 

 prothallium, but the young sporophyte had been destroyed, and 

 there was no means of determining whether this formation of 

 tracheids was associated with apogamy, as in all other similar 

 cases that have been observed. 



The tissues adjacent to the venter of the archegonium grow 

 rapidly, keeping pace with the developing embryo, which 

 becomes very large before it breaks through the overlying 

 tissues (calyptra), which protect it. At this time, the very 

 large foot is especially conspicuous. The root is already some- 

 what elongated and shows a very definite arrangement of its 

 tissues, which resembles that of the later roots. A tetrahedral 

 apical cell is covered by a root-cap composed of several layers 

 of cells, and the axis of the root is occupied by a strand of nar- 

 row cells, which later develop into the vascular cylinder or 

 "stele" of the root. 



The cotyledon, at this time, is relatively inconspicuous, and 

 forms a short, incurved, conical protuberance, between which 

 and the root lies the very slightly conical apex of the shoot. 

 Both stem and leaf show a fairly distinct apical cell, but these 

 apparently cannot be traced back to the original embryo-octants, 

 as is the case in the more specialised Ferns. A very short 

 procambium cylinder can somewhat later be seen in the axis 

 of the stem, and from it extends a similar strand into the cotyle- 

 don. The central cylinder of the stem (Jeffrey (i), p. 21) 

 becomes fully developed below the point of origin of the 

 cotyledon. From the first it is a hollow cylinder with a well- 



