10 



under-surface, with white or yellow meal. The 

 rachises and stipes may also be covered with 

 hairs and scales. 



Venation. The venation or the mode of 

 arrangement of the veins in the fronds often 

 form an important criterion for distinguishing 

 ferns. [Plate V.] The midrib of a simple 

 frond or of the pinnae or pinnules of a compound 

 frond is called the costa. The first branches 

 of the midrib are called veins and the branches 

 proceeding from the veins, veinlets. Veins or 

 veinlets are spoken of as free when they aie 

 unconnected with the neighbouring ones ; anas- 

 tomosing when the veinlets of one vein are con- 

 nected with those of the next ; reticulate when 

 they anastomose so as to form a net-work. 

 Free veins are either simple or branched. 

 Branched veins may be either (a) forked when 

 they break up into two or more branches after 

 leaving the costa ; (b) pinnate when they run 

 from the costa to the margin giving off branch- 

 es on both sides ; or (c) radiate when the veins 

 spread out from a definite point at the base of 

 the frond. Areoles or meshes a/e spaces formed 

 by the anastomosing of veins. Veins or veinlets 

 are said to be cxcurrent when directed towards 

 the margin and recurrent when directed away 



