14 ON GENERA AND SPECIES. 



fascicle terminate before reacHing, or at the margin, their 

 apices being free and unconnected ; and anastomosing when 

 the apices of the branches of each proximate fascicle unite 

 with one another, which they do in various ways, forming 

 regular, square, rhomboid, hexagonal, or unequal sided 

 meshes (areoles). When the primary veins are not evident, 

 and all the anastomoses of about equal size, it is termed 

 reticulate venation. 



Both free and anastomosing veins are spoken of as 

 follows : — Simple, when each vein proceeds from the costas 

 to the margin without branching. Forlced, when they 

 divide at an acute angle into two or more branches, after 

 leaving the costse. Pinnately forked, when the primary 

 veins are scarcely defined, the venules dichotomously 

 branching. Pinnate, when the primary veins that run 

 from the costa? to the margin are distinctly defined, and 

 produce venules in regular order on both sides, forming a 

 more or less acute or oblique angle with their axis. 



The simplest form of anastomosing venation is when the 

 apices of simple or forked veins are combined or connected 

 by means of a vein close to and continuous with the mar- 

 gin, as in the genera Olfersia and Neottopteris. Pinnate and 

 pinnately-forhed veins anastomose by the uniting of the 

 apices of the venules of the proximate fascicles, which they 

 do at various angles, from acute to nearly a right angle, or 

 even arcuate as in Meniscium, or straight as in Blechnum. 



In most of these cases, the connected venules produce from 

 the apex of their angular junction, or from their exterior 

 sides, one or more outward directed veinlets (eoxurrent) 

 which are either free or unite with the next exterior anas- 

 tomose, thus forming in the latter case two or more rows 

 of areoles between the primary veins. When anastomose 

 venules form a right or nearly a right angle with the 



