770 PROFESSOR W. C. WILLIAMSON AND DR. D, H. SCOTT ON THE 
existing Cycadex. The search for “missing links” has met with little encourage- 
ment of late years, and we now realize how much the chances are against our 
lighting on the direct ancestors of living forms. We believe, however, that in 
Lyginodendron and Heterangium we have examples of Fern-like plants of a primitive 
type, which have undergone modifications of the same kind as those to which the 
Cycadeze owed their origin. 
How far, in the case of these genera, such modification had proceeded cannot be 
determined until their reproductive organs have been found. Possibly these plants 
had only varied in their vegetative characters and still retained an essentially Fern- 
like fructification; possibly, on the other hand, they had already acquired some 
Gymnospermous type of reproductive organs. As to all this we know nothing. All 
we can say is, that such divergence from a Fern-type, as is actually shown by the 
known characters, is distinctly in a Cycadean direction. 
Our view as to Lyginodendron and Heterangium is in essential agreement with 
that of Count Sorms-LausacH, who has described in Protopitys Bucheana another 
of these types, intermediate between Filicineze and Gymnosperms.* 
We think it very probable that Poroxylon, so beautifully investigated by 
MM. Berrranp and RENAULT, will find its place in a similar intermediate position. 
In many respects the similarity of structure between this genus and Lyginodendron 
is quite unmistakable, extending even to minute anatomical details, and we think it 
not unlikely that the agreement may turn out to be even closer than appears from 
the statements of the authors. Poroaylon certainly approaches Cycads more closely 
than Lyginodendron does. SEwarp’s Rachiopteris Williamsoni,t as well as 
Myeloxylon, must probably be added to the list. As to Sigillariopsis, we prefer not 
to express any opinion. 
We think the existence of a fossil group on the borderland of Ferns and Cycadeze 
is now well established. The relation of these forms to those very ancient Gymno- 
sperms, the Cordaitez, is a difficult and most interesting question, which cannot, 
however, be discussed here.{ 
The photographic illustrations to the present paper (Plates 18-20) are the work 
of the late Mr. W. Kirman, formerly of the Royal College of Science, London. 
The camera-lucida drawings, reproduced in Plates 21-29, like those in our former 
joint papers, were made by Mr. GrorcE BREBNER. 
* ‘Bot. Zeitung,’ 1894, Abth. 1, p. 206. 
+ ‘Ann. of Bot.,’ vol. 8, 1894, 
_ £ Nors.—In Memoir IX. (p. 352, Plate 25, figs. 90-92) a remarkable piece of stem from the volcanic 
ash of Arran was described under the provisional name of Lyginodendron (P) anomalum. We have 
nothing to add, except that we do not now think the fragment has anything in common with the genus 
Lyginodendron, and would rather suggest a comparison with a Cycadeowylon, figured by M. Ranaut 
(‘Structure comparée de quelques tiges,” &c., Plate 14). 
