1(5 ON GENERA AND SPECIES. 



and opaque. In form they are globose, oval or pyriform, 

 pedicellate or sessile, arid are either furnished with a more 

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

 titute of a ring (exannulate) . 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 (apicafy ; 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. 



Exannulate spore cases are in texture coriaceous becom- 

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

 synangia, 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 Dancece, or separate 

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

 The cells open by slits or pores. 



N.B. About thirty species which constitute the order 

 Marattiacece have exannulate sporangia. 



SORI. 



The sori are masses of sporangia produced on the recep- 

 tacle. Their form and position correspond with, and are 



