16 | ON GENERA AND SPECIES. 
and opaque. In form they are globose, oval or pyriform, 
pedicellate or sessile, and are either furnished with a more 
lor less complete articulated elastic ring (annulate), or des- — 
ltitute of a ring (exannulate). This ring is said to be 
Lang 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 
Es 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. [ 
Ezannulate spore cases are in texture coriaceous becom- a 
ing horny. They are either free, or counate and called - 
synangia, which are formed of a greater or lesser number 2 
of exannulate sporangia, laterally united, forming a series 2 
of cells, disposed in a circle or in two rows, side by side, 4 
which either remain united as in Danew, or separate 3 
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 - 
Marattiacee have exannulate sporangia. 2 
SORI. 
The sori are masses of sporangia produced on the recep- 
tacle. Their form and position correspond with, and are 
