I'TKRIDOPHYTES 



149 



pteridophytes, but is noteworthy in the fact that its neck canal cells are 

 reduced to two in number. 



Embryo. —The development of the embryo differs from that of the 

 Lycopodiales in several particulars. There is no suspensor, and the 

 fertilized egg divides into quad- 

 rants, among which all the body 

 regions are distributed ; foot and 

 root being developed by the inner 

 quadrants, and stem and leaf by 

 the outer ones (figs. 350, 351). A 

 very heavy calyptra is formed, 

 which is broken through by the 

 vigorous young shoot. 



Conclusions. — The sporophyte 

 is to be regarded as highly special- 

 ized in its leaves, stem anatomy, 

 and strobilus; but its embryogeny 

 appears to be simpler than among 

 Lycopodiales. The gametophyte 



is entirely aerial; certain antheridia show a specialized form of develop- 

 ment ; and the archegonia are well advanced, as indicated by the 

 reduction of the neck canal cells. 



351 



Figs. 350, 351. — Embryo of Equisctum: 

 350, early stage of embryo, the four body 

 regions having begun to develop; the 

 general structure of the archegonium still 

 evident; 351, more advanced embryo, 

 showing the apical cell that is developing 

 the stem. — After Sadebeck. 



(5) Ophioglossales 



General character. — This group of pteridophytes is associated often 

 with Filicales. The three genera usually recognized are Ophioglossum 

 (adder's tongue, fig. 352), Botrychium (moonwort, fig. 353), and Hel- 

 minthostachys (a New Zealand genus with a single species, fig. 354)-' 

 The distinguishing character of the group is the so-called fertile spike 

 (a stalk bearing the sporangia), which arises from the adaxial face of 

 the leaf. 



Sporophyte. — The sporophyte consists of a subterranean stem covered 

 by the leaf bases, and there are no aerial branches. The leaves are 

 relatively few in number and large, especially in Botrychium, and de- 

 velop very slowly, in some cases becoming aerial only after two or three 

 years of subterranean development. The vascular cylinder is remark- 

 ably advanced in structure. It is not only a siphonostele (containing 



1 A fourth genus (Sceptridium) has been suggested, including some of the species 

 usually referred to Botrychium. 



