690 TRANSACTIONS OF SECTION K. 
TUESDAY, AUGUST 6. 
The following Papers were read :— 
1. The Real Nature of the so-called Tracheids of Ferns. 
By D. T. Gwynne VauGuan, J/.A. 
The metaxylem elements of the Osmundace, both recent and fossil, are not 
tracheids, but form a special and peculiar type of vessel. The pits, both in the 
end and in the lateral walls, are true perforations, and usually more than one 
series of pits occurs on the same side of the wall. Further, there is no middle 
substance in the median plane of the wall joining together the pairs of bars of 
thickening that separate the corresponding pits of two adjoining tracheids. There 
is therefore a cavity or free passage up and down connecting each vertical series 
of pits in the middle of the substance of the wall. 
These cavities arise by the re-absorption in these regions of the whole of the 
primary wall of the young trachee. The same type of element seems to be 
widely spread among the other orders of the Pteridophyta. 
2. On the Structure and Affinities of Physostoma elegans (Williamson), 
a Pteridospermous Seed from the Coal Measures. By Professor F. W. 
Outver, I.R.S. * 
The diversity of form usually met with in a modern group of plants, such as a 
natural order of Angiosperms, is of great assistance in determining the affinities 
of the group. The differing floral characters of a series of allied genera, for 
instance, furnish the data upon which judgments can be based as to the probable 
line or lines of floral evolution within and even beyond the limits of the order. 
In this respect the palzo-botanist who studies petrifactions is at a disadvantage 
owing to the very isolated and specialised character of the floras that are available. 
Thus the position in regard to the coal-measure flora is somewhat analogous to 
that which would obtain in regard to the existing flora were the latter represented 
by a portion of a single forest and a salt-marsh. Or, to put the matter in a 
slightly different way, our carboniferous petrifactions are largely isolated and often 
special types comparable with Ginkgo, Welwitschia, and Taxus in the existing flora. 
In these circumstances, in the rare cases in which a series of allied forms 
is available, the detailed comparison of its members is most desirable. Such a 
series is afforded by the Lagenostoma-group of pteridospermous seeds of which 
the seed Physostoma elegans’ is one of the representatives. The present paper 
deals with Physostoma and with a consideration of its relationship to the Lageno- 
stomas, The seed is quite exceptional among structures of this class in the 
ensemble of unique and curious characters which it presents. The grounds are 
considered fully for regarding it as the most primitive of the pteridospermous 
seeds that have yet come under observation. 
3. On the Cone of Bothrodendron mundum. 
By D. M. 8. Watson, B.Se. 
The small cone described by Williamson in 1880, part x. of his ‘Memoirs on 
the Organisation of the Fossil Plants of the Coal Measures,’ pl. 15, fig. 8, has been 
obtained in transverse section by the author. The wood of its axis agrees exactly 
with that of Bothrodendron mundum (Will). 
1 This name was originally proposed by the late Professor W. C. Williamson for 
the seed which, owing to the imperfect material then available, he afterwards called 
Lagenostoma physoides. ‘Che time has now arrived when effect may be given to 
Williamson’s original intention. 
