1895.] Lyginodendron and Heterangium. 203 



and phloem are perfectly preserved ; the latter is of great thickness, 

 almost equal to that of the secondary wood. So perfect is the preser- 

 vation, that stages in the development of the tracheides from the 

 cambium have been observed, while the compound sieve-plates on 

 the radial walls of the sieve-tubes are quite clear. Sclerotic groups 

 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 Heterangium, which differs in 

 some respects from the two species above described, and may turn 

 out to represent a third type. 



III. Affinities of 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.* 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. 



In various respects Lyginodendron and Heterangium have points in 

 common with Gleicheniacese, Osmundacese, Marattiaceee, Ophioglosseee, 



* See Zenetti, ' Botanische Zeitung,' 1895. 



