66 On the Structure and Affinities of ["S'ouSA'S'rS' 
of micro-spectroscope at the earnest request of our excellent secretary, 
Mr. Hogg, who is of opinion that the price of the instrument pre- 
viously has prevented its adoption. 
II. — On the Structure and Affinities of some Exogenous Stems 
from the Coal-measures. By W. C. Williamson, F.E.S., 
Professor of Natural History in Owen's College, Manchester. 
The generic term Dadoxylon, orginally introduf!ed by Endlicher, 
has long been used in a vague manner by phytologists. It has 
been applied to a large number of woody stems, common in the 
Coal-measures, very few of which have any claim to rank in the 
genus. As defined by Endlicher and Brongniart, the genus is 
characterized by " les rayons meduUaires etroits, simples composes 
d'une seule lame de tissu cellulaire ; " and further, it has " les 
ponctuations des fibres ligneuses disposees en plusieurs series alter- 
nantes entre elles, et prenant par pression la forme d'areoles 
hexagonales." * 
In 1851 1 described the structure of some forms of Stembergi8e,t 
and pointed out the apparently coniferous character of the woody 
zone surrounding the pith. I demonstrated the existence of rows 
of discs on the woody fibre arranged as in the living conifers ; and 
concluded that the plants under consideration were true examples 
of Endlicher's genus Dadoxylon. Since the publication of that 
memoir, numerous specimens of woody stems have been found, 
EXPLANATION OF PLATE XX. 
-Vertical section of two fibres of Dadoxylon, from Coalbrook Dale. 
-Tangential aspects of the same. 
-Vertical section of part of a reticulated vessel of Dictyoxylon OldJuimium. 
Mr. Butterworth's cabinet. 
-Tangential section of two vessels of the same, separated by a medullary 
ray. 
-Varieties of discs from the vessels of Cycas revoluta. 
-A vessel from the same. 
a. pitted tissue. 
6. glandular discs. 
-Fragment of a stem of Dictyoxylon, reduced one-half. 
-Reticulated fibre from a tangential section of Araucarla imhricata. 
-Fibre from a tangential section of Thuja Donniana. 
-Part of a scalariform vessel from the inner cylinder of a Lepidodendroid 
plant, 
-Vertical section of a Dictyoxylon, showing the Sternbergian pith. Mr. 
Butterworth's Cabinet. 
-Portion of Fig. 10 further magnified. 
Fig. 1.- 
" t 
„ o. 
„ 4.- 
„ 5.- 
„ 6.- 
7. - 
8. - 
9. 
10. 
11. 
12. 
* 'Tableau des Genres de Vegetaux Fossiles,' par Adolphe Brongniart, p. 76. 
t 'Transactions of the Literary and Philosophical Society of Manchester.' 
