ORGANOGRAPHY. 
51 
Axillary when on the point where the veins fork (131). 
Compital when on the angular crossings or points of confluence of 
two or more venules or veinlets. 
Medial when in none of the above positions, but some intermediate 
part of the veins or the branches (21, 28). 
They are superficial, or immersed in the substance of the frond, 
or elevated above its surface, and then columnar (plate I. fig. 9) or 
globose. 
In form they are — 
Pundiform when small and dot-like. 
Elongated when long and line-like. 
Amorphous when of no defined form (46). 
2. Sporangium. 
The spore-cases, or sporangia, are the organs which contain the 
reproductive spores, and are borne in masses upon the receptacles. 
They are thin and transparent, or horny and opaque, unilocular 
and globose, oval or pyriform, usually pedicellate, which is articulate, 
but sometimes sessile, and either furnished with a more or less 
complete articulated elastic ring ( annulate ) (plate I. fig. 1), or 
destitute of a ring ( exannulate ) (plate I. fig. 4). In annulate 
sporangia the ring is said to be 
Vertical when it rises immediately from the apex of the pedicel (of 
which is a continuation), and passes vertically over the apex 
of the sporangium (plate I. fig. 1). 
Horizontal when it passes horizontally round the sporangium 
either at or about its middle (plate I. fig. 2j, or at the apex 
(i apical) (plate I. fig. 3.) 
Oblique when it has neither of the above directions, but passes 
round the sporangium in some direction intermediate 
between them. 
When the sporangia arrive at maturity and are under certain 
favourable conditions as to dryness, the elasticity of the ring causes 
them to burst open with force and sound sufficient to be heard, and 
this takes place in a direction at or very near to a right angle with 
the direction of the ring. In exannulate sporangia the opening 
takes place by a simple slit or pore (plate I. figs. 4 and 5). 
E 2 
