PTERIDOPHYTES 
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 FlGS ' 35. 35 1 - ~ Embryo of Equisetum: 
. , i , , i-ii .1 35. ear 'y sta S e f embryo, the four body 
is to be regarded as highly special- regions having begun to develop; the 
ized in its leaves, Stem anatomy, general structure of the archegonium still 
andstrobilus; but its embryogeny evident ; 35'. mor e 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 (moon wort, 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. 
