THE PTERIDOPHYTA : FILICALES, THE FERNS 



539 



times abortive), the oosphere and the ventral canal cell. The upper one forms 

 a three-tiered neck, which scarcely rises above the surface of the prothallus. 

 The lowest forms the base of the archegonium, and with the prothallus cells 

 helps to form the wall of the venter. 



The embnyo has only a ver\^ small foot, and the stem apex turns round 

 and penetrates the prothallus to the upper surface, where the first leaf 

 appears as if growing from the surface of the prothallus itself (Fig. 538). 



Taking Marattia as a type of the Eusporan- 

 giatae it is of interest to note the characters in 

 which that group show an approach tow^ards the 

 Spermatophyta. These are : — 



1. Massive sporangia. 



2. Diarch primary root in the embryonic 



plant, the production of which is as- 

 sociated with two primary leaves or 

 cotyledons. 



3. Prolonged prothallial nutrition of the 



embr}o in contrast to an earlv 

 liberation of the embr\'o, as in other 

 Pteridophyta. 



4. Rotation of the embryo so that the root 



pole faces the archegonial apex, the 

 position normal in Seed Plants. 



We have ground, therefore, for supposing 

 that although in some respects more primitive 

 than the Leptosporangiatae, the Eusporangiatae ^^G-s^^.—Angioptensteyssman- 



. , 1 . . r 1 T^ • I mana (a genus closely allied 



Stand closer to the origm 01 the rteridospermae to Marattio). Prothallus 



than do the former group, which is more showing perforation by first 



... , , • 1 T-i -1 1 -I- l^af of developing embrvo. 



specialized along strictly rtendophytic lines. {After Goebel.) 



Eusporangiatae : Ophioglossaceae 



In the Ophioglossaceae the stems are subterranean, the aerial portion only 

 consisting of a single leaf which branches into a sterile lamina and a fertile 

 spike on which the sporangia are formed marginallv. The sporangia are 

 homosporous and eusporangiate. The prothalli are subterranean and 

 saprophytic. 



Botrychium lunaria (Moonwort) 



Botrychiiim /iinaria is a rather uncommon British plant, usually found 

 in sub-alpine pastures (Fig. 539). The stem forms a short rod, rarely 

 branched, and usually only an inch or two long, which is found upright 

 beneath the soil. It bears rather thick adventitious roots and is covered with 

 old leaf bases. At its upper end arises a single leaf, 6 to 9 in. long, with a 

 sheathing base. The single petiole bears two distinct leaf segments : one 



