208 Seward ’ — Rachiopteris Williamsoni sp. nov ., 
liamsoni 1 . These slides were prepared from the same speci- 
men from which Williamson’s Figs. 7, 8, and 17 were drawn, 
and which he referred to the genus Myelopteris ( Stenzelia , 
Goeppert, Myeloxylon, Brong). On suggesting to Professor 
Williamson that the sections differed in certain important points 
from the typical Myeloxylon structure, he re-examined them 
and agreed that they should be referred to another plant. 
In Myeloxylon , it will be remembered, we have fragments 
of petioles showing a number of scattered vascular bundles 
embedded in a parenchymatous fundamental tissue in which 
are distributed numerous secretory canals ; towards the peri- 
phery there is a characteristic form of hypodermal tissue, 
consisting of alternating bands of sclerenchymatous fibres and 
thin-walled parenchymatous cells. The vascular bundles are 
of the collateral type, and resemble those of cycadean petioles 
in the fact that the protoxylem is on the side of the xylem 
facing the phloem. In discussing the affinities of the genus, 
the conclusion was arrived at that Myeloxylon ‘ probably 
occupies a position between Cycads and Ferns, but nearer to 
the former than to the latter.’ Professor Stenzel, in referring 
to the affinities of Myeloxylon and the additional evidence 
afforded by my notes on the English specimens, expresses his 
conviction that the genus should be placed with the Cycadeae 
rather than in a position intermediate between Ferns and 
Cycads 2 . 
The specimens for which the name Rachiopteris Wil- 
liamsoni has been suggested agree with the Myeloxylon petioles 
in the possession of the characteristic hypodermal tissue, and 
also in the general disposition of the vascular bundles in the 
fundamental parenchyma. On the other hand, the bundles 
are concentric and not collateral in form, and in addition to 
the reticulate, scalariform, and spiral tracheids, there is a con- 
siderable development of xylem-parenchyma. Another dis- 
tinctive feature of Rachiopteris Williamsoni is the presence of 
a number of canals, arranged at fairly regular intervals in the 
1 Proc. Camb. Phil. Soc., Vol. viii. pt. ii. 1894, p. 41. 
2 Letter from Prof. Stenzel, May, 1893. 
