Si8 



A TEXTBOOK OF THEORETICAL BOTANY 



The early development of the sporangia does not differ essentially from 

 that in other Leptosporangiatae. The ripe sporangia are broadly rounded 

 and are almost sessile on the receptacle. They have a well-developed annulus 

 which, however, differs from that in Dryopteris, Pteridinm and other Poly- 

 podiaceae in being oblique, that is to say, it does not lie in the plane which 

 intersects the point of attachment of the sporangium but lies obliquely 

 across it, bisecting the sporangial wall into two unequal halves (Fig. 514). 



ANNULUS 



Fig. 514. — Hymenophyllum tunbridgense. Sporangia 

 showing broad oblique annulus. {After Bower.) 



The annulus is a complete circle of uniform cells, only those at the stomium, 

 or point of dehiscence, being as a rule somewhat smaller than the rest. The 

 number of spores in each sporangium is always greater than that in the 

 Polypodiaceae, but is variable, in different species, between 128 and 512, 

 numbers which mark the group as related to the primitive Ferns called by 

 Bower the SimpUces, in which the spore numbers are always high. 



The Gametophyte 



The prothallus consists of a number of green, branched, strap-shaped 

 lobes, one cell in thickness, with a slight increase in thickness at the points 

 on the margins where the antheridia and archegonia are developed (Fig. 515). 

 Its appearance recalls the thallus of some Bryophyta of the Jungermanniales. 

 The earliest stage of the prothallus is the development of a short filament 

 of five or six cells, as in Dryopteris, but in Trichomanes the whole prothallus 



