10 ON GENERA AND SPECIES. 



and opaque. In form they are g-lobose, oval or pj'riform, 

 pedicellate or sessile, and are either furnished with a more 

 or less complete articulated elastic ring (annulate^, or des- 

 titute of a ring (e.eannulate). This ring is said to be 

 vertical when it passes over the apex of the sporangia, 

 being a continuation of the pedicel ; horizontal when it 

 passes horizontally round the sporangium, either at or 

 about its middle, or at the apex (apical) ; oblique when it 

 passes round the sporangium in some direction interme- 

 diate between vertical and horizontal. 



When the sporangia arrive at maturity, and are under 

 certain conditions as to dryness, the elasticity of the ring- 

 causes them to burst open, and the spores are ejected. 

 The opening takes place at or very near to a right angle 

 with the direction of the ring — that is, those having a ver- 

 tical ring burst horizontally, and those with a horizontal 

 ring, by a vertical slit. 



Exannulatp. spore cases are in texture coriaceous becom- 

 ing horny. They are either free, or connate and called 

 synaiigia, which are formed of a greater or lesser number 

 of exannulate sporangia, laterally united, forming a series 

 of cells, disposed in a circle or in two rows, side by side, 

 which either remain united as in Danmce, or separate 

 longitudinally in two valve-like lobes, as in Maratlia. 

 The cells open by slits or pores. 



N.B. — About thirty species which constitute the order 

 Marattlaeea;: have exannulate sporangia. 



SORT. 



The sori are masses of sporangia produced on the recep- 

 tacle. Their form and position correspond with, and are 



