Seward. — On the genus Myeloxylon ( Brong .). 15 
and canals with Marattia and Angiopteris. The general ar- 
rangement of the bundles, as seen in transverse sections of 
Angiopteris- petioles, closely resembles that which we find in 
Myeloxylon ; but this agreement ceases when the individual 
bundles are examined : in the one case we have a typical con- 
centric, in the other a typical collateral bundle. In Angiopteris 
the tracheids do not show any very close resemblance to 
those of the fossil petiole ; the reticulate thickening in the 
latter is characteristic, and differs from the type of tracheid 
characteristic of Ferns. As regards the presence of mucilage- 
or gum -canals in Marattiaceae and Myeloxylon , we do not find 
in the former those large canals, bordered by tangentially 
elongated cells, such as are constantly found in the fossil 
specimens, and which exactly correspond to the canals of 
Cycadean petioles. 
4. Hypodermal tissues. 
It is true that we find in Angiopteris a subepidermal band 
of mechanical tissue, but this is usually continuous and not 
interrupted by radiating groups of parenchyma. 
Renault quotes Angiopteris Brongniartiana , and A. Teis- 
manniana as examples of recent Ferns in which we have a 
more marked separation of thick- and thin-walled tissues ; but, 
on the other hand, we can point to several species of Cycads 
where the hypoderm is of the same type as in Myeloxylon. 
We will next consider the Cycadean affinities of Myeloxylon , 
some of which have been previously dealt with by Schenk. 
1 . The collateral 7 iature of the bundles , and the position of 
the protoxylem. 
This character, so clearly marked in well-preserved speci- 
mens, has been passed over by Renault and other writers. 
It is true, as Solms points out, that this structure is by no 
means unknown among recent Ferns : in addition to the col- 
lateral bundles in the petioles of Ophioglossum and Osmunda , 
Haberlandt 1 has shown that this is a common type in the 
1 Haberlandt, Ueber collateral Gefassbiindel im Laube der Fame (Sitzungs- 
berichte der Math.-Naturwiss. Classe der K. Akad. der Wiss. vol. XXXII. p. 121, 
Abth. I, 1881. Vienna). 
