50 FEENS : BRITISH AND FOEEIGN. 



Armies are the spaces formed by tlie anastomosiBg of veins, and are 

 of various shapes and sizes : those next the costa are called 

 costal armies. 



In speaking of the venules of forked and pinnate veins it is 

 sometimes necessary to indicate a particular one in the fiiscicle : 

 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 ox 



segment ; and 

 Recurrent when directed from the niargiii j 



And their apices are said to be 

 Clavate when thickened like a club, 



PBUCTIPICATIOlf. 



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 AcrostichetB it either covers the whole under surface of 

 the fronds, or is iu irregular undefined patches, and in some other 

 cases, as Botrychium, Osmunda, &c., where the fertile fronds are 

 much contracted, it assumes a spike-Uke or racemose form. 



The terms used in describing the fructification may be classed 

 under four heads : — 1st. Those relating to the receptade ; 2nd. 

 those relating to the sporangium and syrumgium; 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— r 

 Te/rminal when on the points of the veins or their branches (5, 7), 

 h(isal when close to the ccsta (1), 



