50 FERNS : BRITISH AND FOREIGN. 



Areoles 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. 

 Venules 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, &c., 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). 



