572 



FILICALES 



B 



of Gleichenia, it is plain that the sporangia are of the same type, as regards 

 the position of the annulus, though differing in the details ; or the comparison 

 might be extended to the Schizaeaceae on the one hand, or the Hymeno- 

 phyllaceae on the other, as regards the position of the annulus. 



The longitudinal slit of dehiscence traverses the distal part of the 

 annulus, following the median plane of the sporangium, and may extend 



some distance down its peri- 

 pheral side, so that it faces 

 outwards from the receptacle. 

 The orientation of the spor- 

 angia being strictly upon the 

 Gleicheniaceous type, it ap 

 pears that the main difference 

 is that, while maintaining the 

 same position of the annulus, 

 the slit gapes towards the 

 peripheral face of the spor- 

 angium rather than on the 

 central side of it. There is no 

 differentiation of a stomium, 

 but the rupture occurs regu- 

 larly at the distal end (..v, 

 Fig. 320 D). The portions of 

 the annulus on either side of 

 the slit straighten as they dry 

 and .curve outwards in the 

 usual way ; they may even 

 become reflexed, tearing away 

 irregularly from the rest of 

 the wall, or carrying frag- 

 ments of it outwards ; in this 

 state the two flaps may appear 

 like the covers of an open 



A' = vertical section of the' base of the "young receptacle " (r) book. As the lllduratlOll 



showing sporangia (s) in basipetal sequence. C, Z? = mature 



sporangia showing the incompletely indurated annulus, and StOpS short about half-Way 

 distal point of dehiscence (.r). A and Ex about 20. X2^o. 



c and /)x 5 o. down the side, the general 



form of the sporangium is 



not altered by the dehiscence, so as to press upon or displace neighbouring 

 sporangia ; in fact, no elbow-room is required, as in Gleichenia, and this 

 is a distinct advantage in a sorus where sporangia are numerous ; in this 

 we may perhaps see the rationale of the incomplete annulus. No sudden 

 jerks of the annulus have been observed, nor would such jerks be very 

 efficient, since the majority of the spores lie below the flaps of the annulus ; 

 the shedding of the spores seems to be mainly on the principle of the 

 pepper-box. 



D 



FIG. 320. 



Loxsoina Cunninghami, Br. E= young sorus with sporangia 

 still protected by indusium (/, /) ^=sorus rather older, with 

 sporangia (s, s) carried up on the elongated receptacle (ps). 



