74 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
assume this, being convinced that the observations of Professor Renault at Autun 
are accurate ; that able observer is much too cautious to speak so decisively as he has 
done respecting the stems of Sphenophyllum for his evidence to be doubted. He has 
kindly sent me examples of his stems, and they agree closely with my own; so that 
the near affinity of Asterophytlites and Sphenophyllum must now be accepted, not 
as a probable hypothesis, but as a determined fact*. It is equally clear that these 
stems have no relationship to Catamites. M. Grand’Eury some time ago arrived 
at this conclusion at St. Etienne (see ‘ Comptes Rendus,’ tome lxviii., “ Observations 
sur les Catamites et les Asterophytlites ”) from the study of their external forms; 
Dr. Dawson has insisted upon the same distinction in the case of his Canadian 
specimens. Professor Renault writes to me respecting the stems of Sphenophyllum : — 
“ II serait difficile de vous donner la description des details de structure de ces tiges 
curieuses, qui n’ont jamais rien eu de commun avec les Calamites.” I am convinced that 
the same conclusion is true in the case of Asterophytlites. To continue to affirm that 
these plants were the branches and foliage of Calamites in the face of this combined 
testimony of independent observers, whose positions have given them opportunities for 
forming a judgment on the question, will surely be to stultify all scientific testimony. 
But, unfortunately, determining what these plants are not does not tell us what they 
are. Whether or not the so-called Calamites verticillatus was the arborescent stem of 
Asterophytlites , as I have deemed probable, my large specimens of amyeloid roots prove 
that these stems must have attained to a comparatively arborescent form. This con- 
clusion has also been arrived at by M. Grand ’Eury. 
In the disposition of the vessels of their primary triangular vascular bundle they seem 
to me to approach the Lyeopodiacece. In Professor Renault’s specimens the vessels 
forming the extreme apex of each arm of the triangle appear to be more barred than 
reticulated ; and both in his specimens and mine their small size, compared with that of 
the more central vessels, as well as the entire exclusion of all cellular elements from 
the interior of the bundle, are strongly indicative of a genesis like that of the similar 
bundles of the Lycopods. The nearest approach to this structure that I am acquainted 
with amongst the living Lyeopodiacece is seen in the five- or six-angled bundle of 
Psilotum triquetrum ; but in this example the central procambium is not converted into 
vessels, but into a compact rod of thick-walled, permanent prosenchyma. Some of the 
vessels of Psilotum exhibit a remarkable tendency to abandon the scalariform, and 
assume an irregularly reticulate type of structure. The bark of this recent plant affords 
an instructive instance of the differences between the several parts of a continuous tissue 
destined to live under different conditions and to perform different functions. In the 
aerial stem its outer layer consists of long narrow prosenchymatous cells with parallel 
sides. The same tissue in the subterranean axis, now generally regarded as an under- 
ground stem rather than as a root, is composed of very large, coarse, thick-walled, irregular 
* I have already (page 42, note) called attention to the fact that some species of Sphenophyllum, at least, 
exhibit the three superficial grooves of the bark so characteristic of young twigs of Aster ophyllites. 
