The Hymenophyllacece. 113 
lamina are formed. Prantl (’75) regarded this dichotomous venation 
as a primitive character, but Boodle (’00) found that in Adiantum 
reniforme, which has a similarly shaped leaf, the division of the 
petiolar bundle at the base of the lamina was also dichotomous and 
he concludes that “this fact does not favour the view that dichotomous 
venation is, of itself, important evidence of a primitive nature.” 
When, however, we consider the strong general evidence for the 
primitiveness of dichotomous branching in the leaves of ferns, 
referred to in the first lecture, together with the likeness of the 
central type of Hymenophyllaceous stele to that found in the 
Botryopterideae, and finally the practical identity between the 
stem-cylinder and the petiolar cylinder in the species under 
consideration, it is clear that the whole organisation of 
Trichomanes reni for me may be said to stand nearer than that of 
any other fern to the primitive hypothetical type of Filicinean 
e»ui 
Fig. 26. Trichomanes radicans. Stele of rhizome ; the phloem, pericycle 
and endodermis shown only on the right. The smallest elements associated 
with the central parenchyma represent protoxylem : two groups can be made 
out on the left and one on the right, x 114. 
organisation indicated in the first two lectures. The fact that the 
lamina of T. reniforme is four cells thick, lends additional support 
to the belief that this species is a particularly primitive type of the 
