Boodle.—Anatomy of the Hymenophyllaceae . 491 
reduction 1 , and the Hymenophyllaceae as forming a sequence, 
of which species of Hymenophyllum are less extreme types 
than species of Trichomanes 2 . Thus species of Hymeno¬ 
phyllum with T. reniforme are comparatively primitive, while 
other species of Trichomanes are more specialized. This is 
hinted at in the anatomy, because, though sub-collateral 
structure occurs in both genera, further reduction to the 
collateral type appears to occur in Trichomanes only, and in 
the latter genus signs of transition between the two-banded 
and sub-collateral types have disappeared. 
The relationships of the Hymenophyllaceae will be referred 
to in the later paper. 
As the literature has been insufficiently referred to 
above, some of the more important works, which deal 
with the anatomy of the Hymenophyllaceae, will now be 
quoted. 
Von Mohl 3 mentions that in Hymenophyllum and Tricho¬ 
manes the vessels are all united into a central bundle. 
Presl 4 gives a series of diagrams illustrating the arrangement 
of the vascular bundles in the petiole of a large number of 
Ferns, and represents all the Hymenophyllaceae given as 
having a circular vascular bundle. Mettenius 5 refers to the 
occurrence and position of axillary buds in a large number 
of species. He describes the pseudo-veins ( Scheinnerven ), 
and the presence of prosenchyma in the petiolar bundle of 
one or two species of Trichomanes . Of the central strand 
in the stem of the Hymenophyllaceae, he says that it is 
composed chiefly of scalariform elements, and contains also 
annular and spiral elements, always at the periphery, and 
often also in the middle, and, besides these and the scalariform 
elements, elongated thin-walled cells. 
1 l. c., p. 65. 2 1. c., p. 66. 
3 Von Mohl, Ueber den Ban des Stammes der Baumfarne, Vermischte Schriften, 
1845, p. 115. 
4 Presl, Die Gefassb. im Stipes der Fame, Abh. k. Bohm. Ges., v. 5, 1847, 
Tab. 5. 
5 Mettenius, Hymenophyllaceen, Abh. k. Sachs. Ges., vii, 1864, and Ueber 
Seitenknospen bei d, Farnen, 
