Studies on the Venation Pattern in Ferns I. Anastomoses and, other Features in <i>Adiantum incisum</i> forsk. (A. Caudatum Sensu Bedd., Non Linn. Pro Parte)

Abstract

Anastomoses, though infrequent, occur in the dichotomous venation of Adiantum incisum Forsk. Generally more than one anastomosis does not occur in 2 single leaflet, but in three leaflets there were two anastomoses each. The anastomoses are classified into seven types. In Type I two branches of a single vein-dichotomy unite and the branches separate immediately after fusion. Type II anastomosis is similar to Type I but the branches do not separate after confluence. In Type III adjacent branches of two vein-dichotomies unite and separate after a short area of confluence. In Type IV two closely adjacent branches of two vein-dichotomies ale interconnected by a very short transverse commissural vein. Type V is similar to Type IV but the commissural vein is obliquely oriented. Type VI is characterized by the formation of an areole by the union of an unbranched arcuate vein and one of the branches of its sister vein lying above it. The region of confluence is very short and the branches again separate. Type VII is similar to Type VI but the branches do not divide after fusion. Vein approximations have been observed in addition to blind vein-endings, sinus vein-dichotomy, detached vein and marginal blind vein-dichotomy. It has been considered that the separation of Hewurdia to a distinct genus is unjustified. Certain phylogenetic aspects of vein-approximations and anastomoses are discussed.