534 
Note. 
occur in the pericycle, as well as in the cortex, and the leaf-trace 
bundles are in pairs — two points in which this species resembles 
Lyginodendron and differs from H. Grievii. Thus the close .relation- 
ship of the two genera, in spite of the different arrangement of the 
primary wood, comes out even more clearly in this species than in 
H. Grievii. 
We have a single specimen of a Heierangium , which differs in some 
respects from the two species above described, and may turn out to 
represent a third type. 
III. Affinities 0/* Lyginodendron and Heterangium. 
The vegetative organs of these genera show a remarkable com- 
bination of fern-like and cycadean characters. The leaves of Lygino- 
dendron, which are now well known, are so like fern-leaves, not only 
in form and venation but in minute structure, that if they stood 
alone they would, without hesitation, be referred to Filices. Although 
many leaves simulate those of ferns in external characters ( Stangeria , 
Thalictrum , &c.), none are known which at the same time show the 
characteristic anatomy of fern-leaves. Hence we are led to attach 
great weight to the characters of the Lyginodendron foliage. That 
of Heterangium , though less well preserved, was evidently of the 
same type. 
In Heterangium the primary structure of the stem is much like that 
of a monostelic fern such as Gleichenia , but the leaf-trace bundles 
closely resemble the foliar bundles of a Cycad. 
In Lyginodendron the whole structure of the stem suggests a Cycad, 
but with the remarkable peculiarity that the bundles here have the 
structure which in Cycadeae is usually (though not always) limited to 
those of the leaf. The cycadean characters are too marked to be 
accidental, though the general anatomy of Lyginodendron is not 
inconsistent with a close relationship to ferns, for in Osmunda we 
have a monostelic fern, with a large pith, collateral bundles in the 
stem, and concentric ones in the leaf 1 . The mere occurrence of 
secondary growth in a fern-like plant is not surprising, considering 
that it takes place in Botrychium and Helminthostachys at the 
present day. 
1 See Zenetti, Bolanische Zeitung, 1895. 
