50 
FERNS : BEITISH AND FOREIGN. 
Areolcs are the spaces formed by the anastomosing of veins, and are- 
of various shapes and sizes : those next the costa are called 
costal areoles. 
In speaking of the venules of forked and pinnate veins it is 
sometimes necessary to indicate a particular one in the fascicle : 
thus, the — 
Anterior venules are those on that side of the vein next the apex of 
the frond or segment ; and the 
Posterior venules those on the opposite side farther from the apex. 
Yenules and veinlets are likewise said to be — 
Excurrent when directed towards the margin of the frond or 
segment ; and 
Recurrent when directed from the margin ; 
And their apices are said to be 
Clavate when thickened like a club. 
FRUCTIFICATION. 
As a general rule, what is called the fructification of Ferns is 
seated on more or less regularly arranged points or lines on the 
under surface or margin of the fronds, and is usually of well- 
defined form. There are, however, some variations from this. For 
example, in Acrostichece it either covers the whole under surface of 
the fronds, or is in irregular undefined patches, and in some other 
cases, as Botrychium, Osmunda, &e., where the fertile fronds are 
much contracted, it assumes a spike-like or racemose form. 
The terms used in describing the fructification may be classed 
under four heads : — 1st. Those relating to the receptacle ; 2nd. 
those relating to the sporangium and synangium ; 3rd. those 
relating to the sorus; and 4th. those relating to the indusium. 
1. Receptacle. 
The receptacles are the sites upon which the sporangia are seated, 
and are generally either thickened points on, or long thickened 
portions of, some part of the venation. 
In position they are — 
Terminal when on the points of the veins or their branches (5, 7). 
Basal when close to the costa (1). 
