PTERIDOPHYTES 



149 



pteridophytes, but is noteworthy in the fact that its neck_canal_cells_are_ 

 reducfid-io-two-i-n-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. ^— V-^^^^-T^ """ 351 



Conclusions. —The sporophyte Figs. 350, 351. — Embryo of £2«)jriu»t,- 



... , , 1 • 1 , . , 35°. early stage of embryo, (he four body 



IS to be regarded as highly special- „gions having begun to develop; the 



ized in its leaves, stem anatomy, general structure of the archegonium still 



andstrobilus; but its embryogeny <>v'dent; 35 r, more advanced embryo, 



, . , , showing the apical cell that is developing 



appears to be simpler than among the stem. - After Sadebeck. 

 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. 



(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 



' A fourth genus (Scc/Jtridium) has been suggested, including some of the species 

 usually referred to Botrychium. 



